The Protestants and the Catholics disagreed with each other. When the Holy Roman Emperor Ferdinand II of Bohemia attempted to reduce the religious actions of his subjects, it sparked a revolt among Protestants.
The Battle of Nordlingen was fought in 1634. It led to the formation of the alliance between the French, Dutch, and the Swedes.
The Peace of Westphalia was a series of peace treaties that were signed between May and October 1648. It marked the end of the war.
As a result, many cities were destroyed and many people died from the war.
Also as a result of the war, the northern part of Germany stayed Protestant and southern Germany turned to Catholicism.