On 8 October 1619, he agrees to help him under the condition that would allow him to take over Bohemia and were granted electoral voice in the Electoral Council. Philip agreed willingly. To strengthen its position, the emperor was skillful and attracted the sympathies of Juan Jorge de Sajonia, who also detested the Calvinists. However, no support was as decisive as that received from the Emperor of Spain, Felipe III, also of the House of Habsburg, who supported him with 18,000 soldiers. Support to the new emperor soon meant a setback for Protestants, who desperately sought the search for allies. Only the Calvinist Frederick V of the Palatinate (current Rhineland, Germany) accepted.
Towards the middle of the year 1620, the armies of both sides were ready. On the one hand was the army of the Catholic League, made up of 25,000 men (commanded by Maximiliano de Baviera, Johan Tzerclaes, count of Tilly, and the count of Bucquoy), speaking to the Austrian border; While Ambrosio Spinola Doria, mercenary in the service of Spain, would depart to Flanders with other 24,000 to subdue the Palatinate. By the Protestant side, count Enrique de Thurn of Bohemia and his 12,000 men, they prepared the resistance. On June 10, 1620, the first referral army, which had already captured the various letters that the Bohemians were sent to Saxony for help, locking combat at the battle of Sablat, winning it. The impact of the defeat shook the Bohemians, who initially lost all communication with Prague, but manage to compose his army. However, very soon is to expose the Covenant between the German Kingdom of Saxony, Austria and Bohemia, and the Catholic army definitely cut their lines of communication, isolating them. Outnumbered, the Protestants must be locked a battle that do not want (at White Hill, Prague) where the Bohemian army commanded by Christian of Anhalt, Prince of Anhalt – Bernburg, is defeated miserably.