George III's long reign was marked by a series of military conflicts involving his kingdoms, much of the rest of Europe, and places further afield in Africa, the Americas and Asia. Early in his reign, Great Britain defeated France in the Seven Years' War, becoming the dominant European power in North America and India.

 However, many of its American colonies were soon lost in the American Revolutionary War, which led to the establishment of the United States of America. A series of wars against revolutionary and Napoleonic France, over a twenty-year period, finally concluded in the defeat of Napoleon in 1815.