The Thirty Years War was a series of European conflicts that lasted from 1618 to 1648. The battles were mainly fought in Germany. The struggle was initially based on the religious conflicts among Germans by the Protestant Reformation, but it was later influenced by other issues, including dynastic rivalries. There were four periods in the war.
The Bavarian Period (1618-1625). In 1618, in Bohemia (now the Czech Republic and then part of the Holy Roman Empire) there was a Protestant Rebellion against the Habsburg Monarchy that ruled there. The Bohemian Slavs had traditionally been against the Holy Roman Empire, as previously seen in the Hussite Wars of the 15th century. The rebellion was quickly put down by Catholic forces (namely the Holy Roman Emperor-Ferdinand II) who wiped out Protestantism in Bohemia through forcible conversions and the activities of militant Jesuit missionaries.
However, the Thirty Year War didn’t end at this phase because outside forces kept it going. Protestants, particularly in Germany, identified with the Bohemian rebellion, and united against the Holy Roman Catholic Emperor Ferdinand II. Danish Period Denmark and its Protestant king, Christian IV, believed that as Protestantism was wiped out in Bohemia, Ferdinand II would then try to do the same thing in the Holy Roman Empire, particularly in Germany. So, Christian IV sent troops into Germany in support of the Protestant cause and also in the hopes of expanding Danish power. King Christian remarked: ;We are here to defend Protestant liberties. If by Gods will, we should gain some territory, so be it.
; Christian XI’ s Protestant armies were decisively beaten by the Catholic imperial army led by Albert of Wallerstein, a mercenary general who had fought for Ferdinand in the Bohemian phase of the war. It was at this point in the war that the Holy Roman Empires Catholic forces were at the peak of their power, and throughou…