CEVAP:

It was the Protestant uprising of Bohemia in 1618 against the repressive rule of the Habsburg dynasty. The Bohemian revolt became stronger; it gained the support of the Evangelical Union. However, the revolt was suppressed by the Habsburgs following a two-year long military campaign. Staring in 1620 and supported by the Pope, Habsburg Emperor Ferdinand II began to invade the member states of the Evangelical Union. The conflict escalated as the northern Protestant states of Denmark and Sweden joined in. After the French, too, entered in 1635, on the side of the Protestants, all the states in continental Europe joined the war. Thus, the war took its final shape, one in which, apart from numerous middle and small participating states, France and Sweden confronted the Spanish and Austrian Habsburgs.