Ferdinand, in his time of triumph, overreaches himself by publishing in 1629 the Edict of Restitution, which requires that all properties of the Roman Catholic Church taken since 1552 be returned to their original owners.

The edict renews Protestant resistance.

Catholic powers also begin to oppose Ferdinand because they fear he is becoming too powerful.

Invading armies from Sweden, secretly supported by Catholic France, march deep into Germany, winning numerous victories.

The Catholic general Tilly and Sweden's Protestant king, Gustavus Adolphus, are killed in separate battles.

Wallenstein is assassinated on Emperor Ferdinand's orders because he fears his general is becoming too powerful.

After the triumph of the Spanish army over Swedish forces at the Battle of Nordlingen in 1634, a truce is arranged between the emperor and some of the German princes under the Treaty of Prague.

France now invades Germany, not for religious reasons but because the House of Bourbon, the dynastic family of several French and Spanish monarchs, wishes to ensure that the House of Habsburg does not become too powerful.

This invasion is illustrative of the French axiom that Germany must always remain divided into small, easily manipulated states. (Indeed, preventing a united Germany will remain an objective of French foreign policy even late in the twentieth century.)

Because of French participation, the war continues until the Peace of Westphalia is signed in 1648.