The Smalkaldic League was a defensive alliance formed in 1531 by several Protestant princes and cities in the Holy Roman Empire. It aimed to protect their rights and interests against the Catholic Emperor, Charles V, and to support the spread of the Reformation initiated by figures like Martin Luther. The League played a significant role in the religious conflicts of the time, particularly during the Smalkaldic War (1546-1547). Although the League was ultimately defeated, it highlighted the growing tensions between Protestant and Catholic states, influencing the future of religious and political dynamics in Europe.