Religious differences led to riots, civil wars, and international conflicts in Europe during the sixteenth century. In the Holy Roman Empire fighting began in 1546. The initial success of Emperor Charles V led to French intervention on the side of the Protestants, lest the emperor acquire even more power. In 1555 Charles agreed to the Peace of Augsburg, which officially recognized Lutheranism and ended religious war in Germany for many decades. Under this treaty, the political authority in each territory of the Holy Roman Empire was permitted to decide whether the territory would be Catholic or Lutheran. His hope of uniting his empire under a single church dashed, Charles V abdicated in 1556, transferring power over his Spanish and Dutch holdings to his son Philip II and his imperial power to his brother Ferdinand.

In France armed clashes between Catholic royalists and Calvinist antiroyalists occurred in many parts of the country. A savage Catholic attack on Calvinists in Paris on August 24, 1572 — Saint Bartholomew’s Day — occurred at the marriage of the king’s sister Margaret of Valois to the Protestant Henry of Navarre. The Saint Bartholomew’s Day massacre initiated a civil war that dragged on for fifteen years, destroying agriculture and commercial life in many areas.

In the Netherlands the movement for church reform developed into a struggle for Dutch independence. In the 1560s Spanish authorities attempted to suppress Calvinist worship and raised taxes. Civil war broke out from 1568 to 1578 between Catholics and Protestants in the Netherlands and between the provinces of the Netherlands and Spain. Eventually the ten southern provinces came under the control of the Spanish Habsburg forces. The seven northern provinces, led by Holland, formed the Union of Utrecht (United Provinces of the Netherlands) and in 1581 declared their independence from Spain. The north was Protestant, and the south remained Catholic. Hostilities continued until 1609, when Spain agreed to a truce that recognized the independence of the northern provinces.

The era of religious wars was also the time of the most extensive witch persecutions in European history. Both Protestants and Catholics tried and executed those accused of being witches, with church officials and secular authorities acting together. The heightened sense of God’s power and divine wrath in the Reformation era was an important factor in the witch-hunts, as were new demonological ideas, legal procedures involving torture, and neighborhood tensions.