An army of 21,000 Bohemians and mercenaries under Christian of Anhalt was defeated by 23,000 men of the combined armies of Ferdinand II, Holy Roman Emperor, led by Charles Bonaventure de Longueval, Count of Bucquoy, and the German Catholic League led by Johann Tserclaes, later Count of Tilly, at Bílá Hora ("White Mountain") near Prague.

In the early 17th century most of the Bohemian estates, although under the dominion of the predominantly Catholic Holy Roman Empire, had large Protestant populations, and had been granted rights and protections allowing them varying degrees of religious and political freedom.

This led to deep consternation among many Bohemian Protestants, who feared not only the loss of their properties, but also of their traditional semi-autonomy, under which many of the estates had separate, individual constitutions governing their relationship with the Empire, and where the king was elected by the local leaders.

Particularly galling to Protestants were perceived violations of Emperor Rudolf II's 1609 Letter of Majesty, which had ensured religious freedom throughout Bohemia.

King Frederick and his military commander, Prince Christian of Anhalt, had organized a Protestant army of 30,000 men; Ferdinand countered with a force of 25,000, many of them seasoned soldiers, under the capable leadership of Field Marshal Tilly, a Catholic Spanish-Flemish nobleman.

Serving with the Catholic League as an official observer was the future "father of modern philosophy", René Descartes.

[7] After conquering most of western Bohemia, the Imperial army made for Prague, the Bohemian capital, then in rebel hands.

He thus gained an advantageous position on the "White Mountain", actually a low plateau, but had little time to set up defensive works.

After the reverses of the previous several weeks, Christian of Anhalt's army had been reduced to about 15,000 men, with little prospect of victory; the mercenaries on both sides had not been paid in months; and with winter approaching, cold wet weather made for less than ideal combat conditions.

Anhalt tried to relieve the situation by sending forward infantry and cavalry led by his son Christian II.

Tilly and his Imperial cavalrymen advanced with 2,000 Bavarian hussars, steadily pushing Protestant forces back to the Star Palace (just west of Prague), where the rebels tried without success to establish a line of defense.