The 20th century of the Common Era began on January 1, 1901 and ended on December 31, 2000, according to the Gregorian calendar.

The British Empire, the Russian Empire, the German Empire, the Ottoman Empire, and the Austro-Hungarian Empire dissolved in the first half of the century, with all but the British Empire collapsing during the course of World War I. The inter-war years saw the Great Depression cause a massive disruption to the world economy. Shortly afterwards, World War II broke out, pitting the Allied powers (chiefly the Soviet Union, the United Kingdom, and the United States) against the Axis powers (chiefly Nazi Germany, the Empire of Japan, and Italy) which eventually resulted in a total victory for the Allies, but at the cost of over 60 million lives and complete devastation of countless nations. As means to prevent future world wars, the United Nations was formed, however disagreements between the two new superpowers, the Soviet Union and the United States, resulted in the Cold War, which dominated geopolitical life for 40 years. The Soviet Union broke up in 1991, resulting in the United States taking on sole superpower status, although by the end of the century China, India, and the European Union had greatly increased their influence.

The century saw a major shift in the way that vast numbers of people lived, as a result of political, ideological, economic, social, cultural, scientific, technological, and medical change and progress. Terms like ideology, world war, genocide, and nuclear war entered common usage. Scientific discoveries, such as the theory of relativity and quantum physics, drastically changed the worldview of scientists, causing them to realize that the universe was fantastically more complex than previously believed, and dashing the hopes at the end of the 19th century that the last few details of scientific knowledge were about to be filled in. Accelerating scientific understanding, more efficient communications, and faster transportation transformed the world in those hundred years more rapidly and widely than at any time in the past. It was a century that started with horses, simple automobiles, and freighters but ended with luxury sedans, cruise ships, airliners and the space shuttle. Western society's basic form of personal transportation for thousands of years, was replaced by automobiles and buses within the span of a few decades. These developments were made possible by the large-scale exploitation of fossil fuel resources (especially petroleum), which offered large amounts of energy in an easily portable form, but also caused widespread concerns about pollution and long-term impact on the environment. Humanity explored outer space for the first time, even taking their first footsteps on the Moon.
Mass media, telecommunications, and information technology (especially computers, paperback books, public education, and the Internet) put the world's knowledge more widely available to people. Many people's view of the world changed significantly as they became much more aware of the struggles of others and, as such, became increasingly concerned with human rights. Advancements in medical technology also improved the welfare of many people: the life expectancy of the world increased from 35 years to 65 years. Rapid technological advancements, however, also allowed warfare to reach an unprecedented high: World War II alone killed over 60 million people, while nuclear weapons gave humankind the means to destroy itself in a very short period of time. The world also became more culturally homogenized than ever with developments in transportation and communications technology, popular music and other influences of Western culture, international corporations, and what was arguably a true global economy by the end of the century.

Summary

The early arms race of the 20th century escalated into a war which involved many powerful nations: World War I (1914–1918). This war drastically changed the way war was fought, as new inventions such as machine guns, tanks, chemical weapons, and grenades created stalemates on the battlefield and millions of troops were killed with little progress made on either side. After more than four years of trench warfare in western Europe, and 20 million dead, those powers who had formed the Triple Entente (France, Britain, and Russia, later replaced by the United States and joined by Italy) emerged victorious over the Triple Alliance (Germany, Austria-Hungary, and the Ottoman Empire). In addition to annexing much of the colonial possessions of the vanquished states, the Triple Entente exacted punitive restitution payments from their former foes, plunging Germany in particular into economic depression. The Russian Empire was plunged into revolution during the conflict and transitioned into the first ever communist state, and the Austro-Hungarian and Ottoman empires were dismantled at the war's conclusion. World War I brought about the end of the royal and imperial ages of Europe and established the United States as a major world military power.

At the beginning of the period, Britain was arguably the world's most powerful nation. However, its economy was ruined by World War I, and its empire began to shrink, producing a growing power vacuum in Europe. Fascism, a movement which grew out of post-war angst and accelerated by the Great Depression of the 1930s, gained momentum in Italy, Germany and Spain in the 1920s and 1930s, culminating in World War II (1939–1945), sparked by Nazi Germany's aggressive expansion at the expense of its neighbours. Meanwhile, Japan had rapidly transformed itself into a technologically advanced industrial power. Its military expansion into eastern Asia and the Pacific Ocean helped to bring the United States into World War II. Germany was defeated by the Soviet Union in the east and by the D-Day invasion of the United Kingdom, the United States, Canada, and Free France from the west. The war ended with the dropping of two atomic bombs on Japan. Japan later became a U.S. ally with a powerful economy based on consumer goods and trade. Germany was divided between the western powers and the Soviet Union; all areas recaptured by the Soviet Union (East Germany and eastward) were essentially transitioned into Soviet puppet states under communist rule. Meanwhile, western Europe was influenced by the American Marshall Plan and made a quick economic recovery, becoming major allies of the United States under capitalist economies and relatively democratic governments.

World War II left about 60 million people dead. When the conflict ended in 1945, the United States and the Soviet Union emerged as very powerful nations. Allies during the war, they soon became hostile to one other as the competing ideologies of communism and democratic capitalism occupied Europe, divided by the Iron Curtain and the Berlin Wall. The military alliances headed by these nations (NATO in North America and western Europe; the Warsaw Pact in eastern Europe) were prepared to wage total war with each other throughout the Cold War (1947–91). The period was marked by a new arms race, and nuclear weapons were produced in the tens of thousands, sufficient to end most life on the planet had they ever been used. This is believed by some historians to have staved off an inevitable war between the two, as neither could win if their full nuclear arsenals were unleashed upon each other. This was known as mutually assured destruction (MAD). Although the Soviet Union and the United States never directly entered conflict with each other, several proxy wars, such as the Korean War (1950–1953) and the Vietnam War (1957–1975), were waged to contain the spread of communism.

After World War II, most of the European-colonized world in Africa and Asia gained independence in a process of decolonization. This, and the drain of the two world wars, caused Europe to lose much of its long-held power. Meanwhile, the wars empowered several nations, including the UK, U.S., Russia, China and Japan, to exert a strong influence over many world affairs. American culture spread around the world with the advent of Hollywood, Broadway, rock and roll, pop music, fast food, big-box stores, and the hip-hop lifestyle. British culture continued to influence world culture, including the "British Invasion" into American music, leading many top rock bands (such as Swedish ABBA) to sing in English. The western world and parts of Asia enjoyed a post-World War II economic boom. After the Soviet Union collapsed under internal pressure in 1991, a ripple effect led to the dismantling of communist states across eastern Europe and their rocky transitions into market economies.

Following World War II, the United Nations was established as an international forum in which the world's nations could get together and discuss issues diplomatically. It has enacted laws on conducting warfare, environmental protection, international sovereignty, and human rights, among other things. Peacekeeping forces consisting of troops provided by various countries, in concert with various United Nations and other aid agencies, has helped to relieve famine, disease, and poverty, and to contain local wars and conflicts. Europe slowly united, politically and economically, into what eventually became the European Union, which consisted of 15 European countries by the end of the century.

In approximately the last third of the century, concern about humankind's impact on the Earth's environment caused environmentalism to become a major citizen movement. In many countries, especially in Europe, the movement was channeled into politics partly through Green parties, though awareness of the problem permeated societies. By the end of the century, some progress had been made in cleaning up the environment though pollution continued apace. Increasing awareness and pessimism over global warming began in the 1980s, sparking one of the most heated social and political debates by the turn of the century.
Medical science and the Green Revolution in agriculture enabled the world's population to grow from about 1.6 billion to about 6.0 billion. This rapid population increase quickly became a major concern and directly caused or contributed to several global issues, including conflict, poverty, major environmental issues, and severe overcrowding in some areas.

The nature of change

Due to continuing industrialization and expanding trade, many significant changes of the 20th century were, directly or indirectly, economic and technological in nature. Inventions such as the light bulb, the automobile, and the telephone in the late 1800s, followed by supertankers, airliners, motorways, radio, television, antibiotics, frozen food, computers and microcomputers, the Internet, and mobile telephones affected the quality of life for great numbers. Scientific research and technological development was the force behind vast changes in everyday life, to a degree which was unprecedented in human history.

Developments in brief

Wars and politics

• After decades of struggle by the women's suffrage movement, all western countries gave women the right to vote.

• Rising nationalism and increasing national awareness were among the many causes of World War I (1914–1918), the first of two wars to involve many major world powers including Germany, France, Italy, Japan, Russia/USSR, the United States and the British Empire. World War I led to the creation of many new countries, especially in Eastern Europe. At the time it was said by many to be the "war to end all wars".

• Civil wars occurred in many nations. A violent civil war broke out in Spain in 1936 when General Francisco Franco rebelled against the Second Spanish Republic. Many consider this war as a testing battleground for World War II, as the fascist armies bombed some Spanish territories.

• The economic and political aftermath of World War I and the Great Depression in the 1930s led to the rise of fascism and nazism in Europe, and subsequently to World War II (1939–1945). This war also involved Asia and the Pacific, in the form of Japanese aggression against China and the United States. Civilians also suffered greatly in World War II, due to the aerial bombing of cities on both sides, and the German genocide of the Jews and others, known as the Holocaust. In 1945, Hiroshima and Nagasaki were bombed with nuclear weapons.

• During World War I, in Russia the Bolshevik putsch took over the Russian Revolution of 1917, precipitating the founding of the Soviet Union and the rise of communism. After the Soviet Union's involvement in World War II, communism became a major force in global politics, notably in Eastern Europe, China, Indochina and Cuba, where communist parties gained near-absolute power. This led to the Cold War and proxy wars with the West, including wars in Korea (1950–1953) and Vietnam (1957–1975).

• The Soviet authorities caused the deaths of millions of their own citizens in order to eliminate domestic opposition. More than 18 million people passed through the Gulag, with a further 6 million being exiled to remote areas of the Soviet Union.

• The civil rights movement in the United States and the movement against apartheid in South Africa challenged racial segregation in those countries.

• The two world wars led to efforts to increase international cooperation, notably through the founding of the League of Nations after World War I, and its successor, the United Nations, after World War II.

• The creation of Israel, a Jewish state in the Middle East, by the British Mandate of Palestine fueled many regional conflicts. These were also influenced by the vast oil fields in many of the other countries of the mostly Arab region.

• The end of colonialism led to the independence of many African and Asian countries. During the Cold War, many of these aligned with the United States, the USSR, or China for defense.

• After a long period of civil wars and conflicts with European powers, China's last imperial dynasty ended in 1912. The resulting republic was replaced, after yet another civil war, by a communist People's Republic in 1949. At the end of the century, though still ruled by a communist party, China's economic system had transformed almost completely to capitalism.

• The Great Chinese Famine was a direct cause of the death of tens of millions of Chinese peasants between 1959 and 1962. It is thought to be the largest famine in human history.

• The Tiananmen Square protests of 1989, culminating in the deaths of hundreds of civilian protestors, were a series of demonstrations in and near Tiananmen Square in Beijing,China. Led mainly by students and intellectuals, the protests occurred in a year that saw the collapse of a number of communist governments around the world.

• The revolutions of 1989 released Eastern and Central Europe from Soviet supremacy. Soon thereafter, the Soviet Union, Czechoslovakia, and Yugoslavia dissolved, the latter violently over several years, into successor states, many rife with ethnic nationalism. East Germany and West Germany were reunified in 1990.

• European integration began in earnest in the 1950s, and eventually led to the European Union, a political and economic union that comprised 15 countries at the end of the century.

Culture and entertainment

• As the century began, Paris was the artistic capital of the world, where both French and foreign writers, composers and visual artists gathered.

• Movies, music and the media had a major influence on fashion and trends in all aspects of life. As many movies and much music originate from the United States, American culture spread rapidly over the world.

• Computer games and internet surfing became new and popular form of entertainment during the last 25 years of the century.

• In literature, science fiction, fantasy (with well developed, rich in details fictional worlds), alternative history fiction gained unprecedented popularity. Detective fiction gained unprecedented popularity between the two world wars.

• Blues and jazz music became popularized during the 1910s and 1920s in the United States. Blues went on to influence rock and roll in the 1950s, which only increased in popularity with the British Invasion of the mid-to-late '60s. Rock soon branched into many different genres, including heavy metal, punk rock, and alternative rock and became the dominant genre of popular music. This was challenged with the rise of hip hop in the 1980s and 1990s. Other genres such as house, techno, reggae, and soul all developed during the latter half of the 20th century and went through various periods of popularity.

• In classical music, composition branched out into many completely new domains, including dodecaphony, aleatoric (chance) music, and minimalism.

• Synthesizers began to be employed widely in music and crossed over into the mainstream with new wave music in the 1980s. Electronic instruments have been widely deployed in all manners of popular music and has led to the development of such genres as house, synthpop, electronic dance music, and industrial.

• The art world experienced the development of new styles and explorations such as expressionism, Dadaism, cubism, de stijl, abstract expressionism and surrealism.

• The modern art movement revolutionized art and culture and set the stage for both Modernism and its counterpart postmodern art as well as other contemporary art practices.

• In Europe, modern architecture departed radically from the excess decoration of the Victorian era. Streamlined forms inspired by machines became more commonplace, enabled by developments in building materials and technologies. Before World War II, many European architects moved to the United States, where modern architecture continued to develop.

• After gaining political rights in the United States and much of Europe in the first part of the century, and with the advent of new birth control techniques, women became more independent throughout the century.

• The automobile vastly increased the mobility of people in the Western countries in the early to mid-century, and in many other places by the end of the century. City design throughout most of the West became focused on transport via car.

• The popularity of sport increased considerably—both as an activity for all, not just the elite, and as entertainment, particularly on television.

Science

• Starting with invention of Turing machine, new fields of mathematics studying computability and computation complexity were developed.

• Gödel's incompleteness theorems were formulated and proven.

• New areas of physics, like special relativity, general relativity, and quantum mechanics, were developed during the first half of the century.

• While some pioneering experiments about internal structure of atoms had been made at the end of XIX century, it is only in XX century the structure of atoms was clearly understood, followed by discovery of elementary particles.

• It was found that all the known forces can be traced to only four fundamental interactions. It was discovered further that two of them, namely electromagnetism and weak interaction, can be merged in the electroweak interaction, leaving only three different fundamental interactions.

• Discovery of nuclear reactions, in particular nuclear fusion, finally solved the problem of the source of solar energy. The age of solar system, including Earth, was determined and it turned to be much older than what was considered before (more than 4 billions years rather than 20 millions years suggested by lord Kelvin in 1862).

• Radiocarbon dating became a powerful technique to determine the age of prehistoric animals and plants as well as historical objects. No such technique existed in XIX century.

• In astronomy, much better understanding of the evolution of the Universe was achieved, its age was determined, the Big Bang theory was proposed. Planets of solar system and their moons were closely discovered. It was found that there is no sentient (or complex animal or plant) life on their surface.

• In biology, genetics was unanimously accepted and significantly developed. The structure of DNA was determined in 1953 by Watson and Criek, following by developing techniques which allow to read DNA sequences and culminating in starting the Human Genome Project (not finished in XX century) and cloning the first mammal in 1996.

• The role of sex reproduction in evolution was understood, and bacterial conjugation was discovered.

Technology

• The number and types of home appliances increased dramatically due to advancements in technology, electricity availability, and increases in wealth and leisure time. Such basic appliances as washing machines, clothes dryers, exercise machines, refrigerators, freezers, electric stoves, and vacuum cleaners all became popular from the 1920s through the 1950s. The microwave oven became popular during the 1980s. Radios were popularized as a form of entertainment during the 1920s, which extended to television during the 1950s. Cable television spread rapidly during the 1980s. Personal computers began to enter the home during the 1970s-1980s as well. The age of the portable music player grew during the 1960s with the development of 8-track and cassette tapes, which slowly began to replace record players. These were in turn replaced by the CD during the late 1980s and 1990s. The proliferation of the Internet in the mid-to-late 1990s made digital distribution of music (mp3s) possible. VCRs were popularized in the 1970s, but by the end of the millennium, DVDs were beginning to replace them.

• The first airplane was flown in 1903. With the engineering of the faster jet engine in the 1940s, mass air travel became commercially viable.

• The assembly line made mass production of the automobile viable. By the end of the century, billions of people had automobiles for personal transportation. The combination of the automobile, motor boats and air travel allowed for unprecedented personal mobility. In western nations, motor vehicle accidents became the greatest cause of death for young people. However, expansion of divided highways reduced the death rate.

• The triode tube (Audion), transistor and integrated circuit revolutionized computers, leading to the proliferation of the personal computer in the 1980s and cell phones and the public-use Internet in the 1990s.

• New materials, most notably plastics, polyethylene, Velcro, and teflon, came into widespread use for many various applications.

• Thousands of chemicals were developed for industrial processing and home use.

• The Space Race between the United States and the Soviet Union gave a peaceful outlet to the political and military tensions of the Cold War, leading to the first human spaceflight with the Soviet Union's Vostok 1 mission in 1961, and man's first landing on another world—the Moon—with America's Apollo 11 mission in 1969. Later, the first space station was launched by the Soviet space program. The United States developed the first (and to date only) reusable spacecraft system with the Space Shuttle program, first launched in 1981. As the century ended, a permanent manned presence in space was being founded with the ongoing construction of the International Space Station.

• In addition to Human spaceflight, unmanned space probes became a practical and relatively inexpensive form of exploration. The first orbiting space probe, Sputnik 1, was launched by the Soviet Union in 1957. Over time, a massive system of artificial satellites was placed into orbit around Earth. These satellites greatly advanced navigation, communications, military intelligence, geology, climate, and numerous other fields. Also, by the end of the century, unmanned probes had visited the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and various asteroids and comets. The Hubble Space Telescope, launched in 1990, greatly expanded our understanding of the Universe and brought brilliant images to TV and computer screens around the world.

Medicine

• Placebo-controlled, randomized, blinded clinical trials became a powerful tool for testing new medicines.

• Antibiotics drastically reduced mortality from bacterial diseases and their prevalence.

• A vaccine was developed for polio, ending a worldwide epidemic. Effective vaccines were also developed for a number of other serious infectious diseases, including influenza, diphtheria, pertussis (whooping cough), tetanus, measles, mumps, rubella (German measles), chickenpox, hepatitis A, and hepatitis B.

• A successful application of epidemiology and vaccination led to the eradication of the smallpox virus in humans.

• X-rays became powerful diagnostic tool for wide spectrum of diseases, from bone fractures to cancer. In the 1960s, computerized tomography was invented. Other important diagnostic tools developed were sonography and magnetic resonance imaging.

• Development of vitamins virtually eliminated scurvy and other vitamin-deficiency diseases from industrialized societies.

• New psychiatric drugs were developed. These include antipsychotics for treating hallucinations and delusions, and antidepressants for treating depression.

• The role of tobacco smoking in the causation of cancer and other diseases was proven during the 1950s (see British Doctors Study).

• New methods for cancer treatment, including chemotherapy, radiation therapy, and immunotherapy, were developed. As a result, cancer could often be cured or placed in remission.

• The development of blood typing and blood banking made blood transfusion safe and widely available.

• The invention and development of immunosuppressive drugs and tissue typing made organ and tissue transplantation a clinical reality.

• Research on sleep and circadian rhythms led to the discovery of sleep disorders.

• New methods for heart surgery were developed, including pacemakers and artificial hearts.

• Cocaine/crack and heroin were found to be dangerous addictive drugs, and their wide usage had been outlawed; mind-altering drugs such as LSD and MDMA were discovered and later outlawed. In many countries, a war on drugs caused prices to soar 10x-20x higher, leading to profitable black market drugdealing, and to prison inmate sentences being 80% related to drug use by the 1990s.

• Contraceptive drugs were developed, which reduced population growth rates in industrialized countries.

• The development of medical insulin during the 1920s helped raise the life expectancy of diabetics to three times of what it had been earlier.

• The elucidation of the structure and function of DNA initiated the development of genetic engineering and the mapping of the human genome.

• Masturbation was found to be a harmless activity. Beliefs that it seriously harms physical and mental health, shared by XIX century physicians, found to be wrong.

• As a result of some of the above developments, most notably antibiotics and vaccines, child and young people's mortality decreased drastically.

Notable diseases

• An influenza pandemic, the Spanish Flu, killed anywhere from 20 to 100 million people between 1918 and 1919.

• A new viral disease, AIDS, arose in Africa and subsequently killed millions of people throughout the world. AIDS treatments remained inaccessible to many people living with AIDS in developing countries, and a cure has yet to be discovered.

• Because of increased life spans, the prevalence of cancer, Alzheimer's disease, Parkinson's disease, and other diseases of old age increased slightly.

• Sedentary lifestyles, due to labor-saving devices and technology, contributed to an "epidemic" of obesity, at first in the rich countries, but by the end of the century, increasingly in the developing world, too.

Energy and the environment

• The dominant use of fossil sources and nuclear power, considered the conventional energy sources.

• Widespread use of petroleum in industry—both as a chemical precursor to plastics and as a fuel for the automobile and airplane—led to the vital geopolitical importance of petroleum resources. The Middle East, home to many of the world's oil deposits, became a center of geopolitical and military tension throughout the latter half of the century. (For example, oil was a factor in Japan's decision to go to war against the United States in 1941, and the oil cartel, OPEC, used an oil embargo of sorts in the wake of the Yom Kippur War in the 1970s).

• A vast increase in fossil fuel consumption caused smog and other forms of air pollution, global warming, local and global climate change.

• Pesticides, herbicides and other toxic chemicals accumulated in the environment, including the bodies of humans and other animals.

• Overpopulation and worldwide deforestation diminished the quality of the environment.

• Rapidly falling fertility rates among Americans and Europeans begin to cause what has been called a "demographic winter," with a possibility of soon bringing these cultures to an end forever.

The world at the end of the century

By the end of the 20th century, more technological advances had been made than in all of preceding history. Communications and information technology, transportation technology, and medical advances had radically altered daily lives. Europe appeared to be at a sustainable peace for the first time in recorded history. The people of the Indian subcontinent, a sixth of the world population at the end of the century, had attained an indigenous independence for the first time in centuries. China, an ancient nation comprising a fifth of the world population, was finally open to the world in a new and powerful synthesis of west and east, creating a new state after the near-complete destruction of the old cultural order. With the end of colonialism and the Cold War, nearly a billion people in Africa were left with truly independent new nation states, some cut from whole cloth, standing up after centuries of foreign domination.

The world was undergoing its second major period of globalization; the first, which started in the 18th century, having been terminated by World War I. Since the U.S. was in a position of almost unchallenged domination, a major part of the process was Americanization. This led to anti-Western and anti-American feelings in parts of the world, especially the Middle East. The influence of China and India was also rising, as the world's largest populations, long marginalized by the West and by their own rulers, were rapidly integrating with the world economy.
Terrorism, dictatorship, and the spread of nuclear weapons were some issues requiring attention. The world was still blighted by small-scale wars and other violent conflicts, fueled by competition over resources and by ethnic conflicts. Despots such as Kim Jong-il of North Korea continued to lead their nations toward the development of nuclear weapons.

Disease threatened to destabilize many regions of the world. New viruses such as SARS and West Nile continued to spread. Malaria and other diseases affected large populatios. Millions were infected with HIV, the virus which causes AIDS. The virus was becoming an epidemic in southern Africa.
Some speculate that in the long term, environmental problems may threaten the planet's liveability. One popular belief is that global warming may be occurring, and may be due to human-caused emission of greenhouse gases, particularly carbon dioxide produced by the burning of fossil fuels. This prompted many nations to negotiate and sign the Kyoto treaty, which set mandatory limits on carbon dioxide emissions.

World population

Some believe that significant driver of many of the problems at the end of the 20th century was overpopulation. Yet the 20th century is most notable for the sheer numbers of mass genocide and the killing of over 262 million people by government. See, for example, "Power Kills" and updated statistics for 1900-1999 at the Government action, rather than economic or social conditions, or even international conflict and war, were the driving causes of death in the 20th Century.

Overpopulation has been a fascination of many including economic theorist Reverend Thomas Robert Malthus whose "An Essay on the Principal of Population" was first published in 1798. At the century's end, the global population was 6.1 billion and rising. In the long term, it was predicted that the population would probably reach a plateau of nine billion around 2050.

See also

• 20th century art (with Modern art)

• 20th century events

• 20th century inventions

• Death rates in the 20th century

• Infectious disease in the 20th century

• List of battles 1901-2000

• List of largest optical telescopes in the 20th century

• The individual decades and years