The Schmalkaldic League was a defensive alliance formed in 1531 by several Protestant princes and cities in the Holy Roman Empire. It aimed to protect their interests against the Catholic Emperor Charles V and to support the spread of the Reformation, which was led by figures like Martin Luther. The League was named after the town of Schmalkalden, where the agreement was signed. The League played a significant role in the Religious Wars of the 16th century, particularly during the Schmalkaldic War (1546-1547). Despite initial successes, the League was ultimately defeated by Charles V's forces, leading to the Peace of Augsburg in 1555, which allowed for some degree of religious tolerance within the Empire.