The Battle of Nördlingen (; ; ) was fought on 27 August (Julian calendar) or 6 September (Gregorian calendar), 1634 during the Thirty Years' War. The Catholic Imperial army, bolstered by 18,000 Spanish and Italian soldiers won a great victory in the battle over the combined Protestant armies of Sweden and their German-Protestant allies (Heilbronn Alliance).

After the failure of the tercio system in the first Battle of Breitenfeld in 1631, the professional Spanish and Italians deployed at Nördlingen proved the tercio system could still contend with the deployment improvements devised by Maurice of Orange and the late Gustavus Adolphus of Sweden.

Prelude

After the Protestant victory in the Battle of Lützen two years before, the Swedes failed to follow up their victory due to the death of their king, Gustavus Adolphus. As a result, the Imperial forces had begun to regain the initiative. In 1634 a Protestant Saxon and Swedish army had invaded Bohemia threatening the Habsburg core territories.

The future Holy Roman Emperor, Ferdinand of Hungary decided to attack the Protestant territories in Southern Germany to draw the main Swedish and German armies away from Bohemia. Both sides were aware that Spanish reinforcements under his cousin the Cardinal-Infante Ferdinand were en-route from their dominions in Northern Italy. The Spanish army had marched through the Stelvio Pass trying to open a new 'Spanish Road', and take their Commander to his Governorship of the Spanish Low Countries. The Protestant commanders decided they could not ignore the threat and combined their two largest armies near Augsburg on July the 12th, the Swabian-Alsatian Army under Gustav Horn and the so called Franconian Army under Bernhard of Saxe-Weimar. Both armies were named after their main operation area and belonged to the Heilbronn Alliance (Sweden's german-protestant allies under the directorate of the swedish chancellor Axel Oxenstierna). They were mainly consisting of german and some british mercenaries with a few national swedish/finnish regiments (mostly cavalry) and one national swedish infantry regiment (the yellow regiment).

The Protestants proved unable to prevent the fall of Regensburg to Ferdinand of Hungary and desperately pursued him westwards in an effort to prevent the merger of the two Habsburg armies. On 16 August the Cardinal-Infante crossed the Danube at Donauwörth. Despite their best efforts the Protestant armies were still behind when Ferdinand and the Imperials set down to besiege the town of Nordlingen, in Swabia and await the Cardinal-Infante who arrived before the city on the 2nd September - three days before the Protestants.

Battle

The cousins Ferdinand and Ferdinand prepared for battle, ignoring the advice of the more experienced generals, such as the Imperial general Matthias Gallas. Most of the generals felt a full engagement against two of the most experienced Protestant commanders was reckless and unlikely to have a positive outcome. However the cousins were supported by the Count of Leganés, the Spanish deputy commander. He appreciated that the Catholic army was significantly superior in numbers and had at its core the highly trained professional Spanish Infantry who had not been present at previous Swedish victories over the Imperials.

Bernhard and Horn also prepared for battle, although this may not have been a mutual decision. Bernhard felt that whatever the odds an attempt must be made to relieve Nordlingen. Horn seems to have been reluctant to do so given the ragged state of the Protestant armies. Both commanders seem to have underestimated the numerically superior enemy forces. This may have been due to incorrect reports, or disbelieving those they had received. Whatever the reason Horn and Bernhard estimated that the Spanish reinforcements numbered only 7,000, not 21,000, added to the 12,000 Imperials this gave the Habsburgs a considerable superiority over the 26,000 Protestants.
During the battle, almost anything that could go wrong went wrong for the Protestant forces. This was due to the strong defensive efforts of the Spanish infantry, the feared "Tercios Viejos" (Old Tercios), mainly those commanded by Fuenclara, Idiáquez, and Toralto. Fifteen Swedish assaults by Horn's right wing, consisting of the brigades Vitzthum, Pfuel and the Scots Brigade (Colonel Gunn), supported by the brigade of Count Thurn (Black and Yellow Regiment) on the hill of Albuch, were repulsed by the Spaniards with the decisive support of Ottavio Piccolomini's cavalry squadrons, under direct orders of another Italian commander, the loyal servant to the Spanish Crown, Gerardo di Gambacorta di Linata. On the left of the Protestant line the left swedish wing under Bernhard of Weimar and the Imperial-Bavarian troops had avoided closing with each other, until late in the battle. The Imperial commanders observed the weakened condition of Bernhard's troops, who had been sending large numbers of reinforcements to assist the Swedish troops. They ordered an advance by the Imperial troops which resulted in the quick collapse and rout of the weakened swedish left wing infantry brigades. Pursuit of Bernhard's troops threatened to cut off any escape route of the Swedish units, who also promptly broke, turning into a panic stricken mob and leaving their side of the field to the Spanish and Italian troops of the Cardinal.

Horn was captured, his army was destroyed, and the remainder of the Protestants who successfully fled to Heilbronn were only a remnant of those engaged. The two Ferdinands had achieved a great military victory.

Aftermath

The battle was one of the most crushing defeats the Protestants sustained during the war. The Swedish army in Germany was crippled by the defeat and the battle marked the end of the Swedish attempts to dominate Germany. Meanwhile, the victory led most of the Protestant princes of Germany to seek a separate peace with the Emperor, which was achieved by the Treaty of Prague in 1635.

With Imperial forces threatening dominance in Germany, Spainish troops firmly settled on the western bank of the Rhine, and thus with Habsburg armies surrounding France. Richelieu decided France needed to take a more active role in the conflict, entering the war mainly against Spain and thus opening a second front in the Catholic Low Countries. In the long term the battle did not prove to be a major turning point for Habsburg fortunes, the conclusion of the war in 1648 still ended largely in defeat for the Spanish and Imperials. However, the defeat of the Swedes at Nordlingen was largely responsible for French not Swedish goals taking precedence at the negotiations, with a significant effect on the political map of Germany.