To take advantage of Ferdinand's preoccupation with the Bohemian Revolt at the beginning of the Thirty Years' War, Bethlen invaded Habsburg-controlled Royal Hungary in 1618 and fully conquered it until 1620. Although a peace was settled in January 1620 giving Bethlen 13 counties in eastern Royal Hungary, the prince resumed the war in September. Ferdinand's defeat of the Bohemians at the Battle of White Mountain in November allowed him to focus his forces on Bethlen, and the emperor was able to reconquer most of Royal Hungary by 1621. Because Bethlen did not distribute the confiscated property of Catholic noblemen to his Protestant noblemen as he had promised, they rescinded their support. These setbacks, as well as Bethlen's lack of support from the Ottoman Empire, led Bethlen and Ferdinand to seek terms in Nikolsburg.