elected ruler, regardless of religion. As a result, although Frederick accepted the crown and entered Prague in October 1619, his support gradually eroded over the next few months. In July 1620, the Protestant Union proclaimed its neutrality, while John George of Saxony agreed to back Ferdinand in return for the cession of Lusatia, and a promise to safeguard the rights of Lutherans in Bohemia. Maximilian of Bavaria funded a combined Imperial-Catholic League army led by Count Tilly and Charles of Bucquoy, which pacified Upper and Lower Austria and occupied western Bohemia before marching on Prague. The Bohemians, led by Christian of Anhalt, moved to block the Imperial advance, but was defeated by Tilly at the Battle of White Mountain in November 1620. Although far from decisive, the rebels were demoralised by lack of pay, shortages of supplies, and disease, while the countryside had been devastated by Imperial troops. Frederick fled Bohemia and the revolt collapsed. The Palatinate Campaign By abandoning Frederick, the German princes hoped to restrict the dispute to Bohemia, but Maximilian's dynastic ambitions made this impossible. In the October 1619 Treaty of Munich, Ferdinand agreed to transfer the Palatinate's electoral vote to Bavaria and allow him to annex the Upper Palatinate. Many Protestants supported Ferdinand because they objected to deposing the legally elected king of Bohemia, and now opposed Frederick's removal on the same grounds. Doing so turned the conflict into a contest between Imperial authority and "German liberties", while Catholics saw an opportunity to regain lands lost since 1555. The combination destabilised large parts of the Empire. The strategic importance of the Palatinate and its proximity to the Spanish Road drew in external powers; in August 1620, the Spanish under Spinola and Córdoba occupied the Lower Palatinate. James I of England responded to this attack on his son-in-law by sending naval forces to threaten Spanish possessions in the Americas and the Mediterranean, and announced he would declare war if Spinola had not withdrawn his troops by spring 1621. These actions were primarily designed to placate his opponents in Parliament, who considered his pro-Spanish policy a betrayal of the Protestant cause. However, Spanish chief minister Olivares correctly interpreted them as an invitation to open negotiations, and in return for an Anglo-Spanish alliance offered to restore Frederick to his Rhineland possessions. Since Frederick's demand for full restitution of his lands and titles was incompatible with the Treaty of Munich,