The Twelve Years' Truce was the name, given later, to the 12-year period of
ceasefire within the Eighty Years' War in the Netherlands
from March 1609-1621,

between the United Provinces and the Spanish controlled southern states,
mediated by France and England at The Hague. It was during this ceasefire, the Dutch made great efforts to build their navy, which was later to have a crucial bearing on the course of the war.

During the Truce, two factions emerged in the Dutch camp, along political and religious lines. On one side were the Arminians, whose prominent supporters included Johan van Oldenbarnevelt and Hugo Grotius.
They tended to be well-to-do merchants who accepted a less strict interpretation of the Bible than did classical Calvinists. They were opposed by the more radical Gomarists, supported by Maurice of Nassau. In 1617 the conflict escalated when republicans pushed the "Sharp Resolution", allowing the cities to take measures against the Gomarists. Prince Maurice accused van Oldenbarnevelt of treason, had him arrested, and in 1619, executed. Hugo Grotius fled the country after escaping from imprisonment in Castle Loevestein.