Protestant Union, in German history, an alliance of German Protestant leaders of cities and states, founded in 1608 for the avowed purpose of defending the lands, person, and rights of each individual member. Also known as the Evangelical League, it came into being after the Holy Roman emperor attempted (1607) to reestablish Roman Catholicism in Donauwörth and after a majority of the Reichstag, meeting in Augsburg, declared that renewal of the religious peace of 1555 (see Augsburg, Peace of) should be conditional on the restoration of all church lands appropriated by the Protestant princes after 1552. A Catholic League, headed by Duke Maximilian I of Bavaria, was formed shortly afterward. The Protestant Union was weakened from the start by the absence of such powerful Protestant princes as the elector of Saxony, and it never operated very effectively. In 1621, three years after the outbreak of the Thirty Years War, the union went out of existence. In French history, the alliance (1573–74) of Huguenot cities, districts, and nobles in the Wars of Religion is also known as the Protestant Union.