The event that ignited the American Revolutionary War in 1775 was the battles of Lexington and Concord on April 19. Tensions had been escalating between colonial militias and British troops due to issues like taxation without representation, the Intolerable Acts, and a growing desire for independence. When British soldiers aimed to confiscate colonial arms and arrest revolutionary leaders, they encountered armed resistance. The skirmishes marked the transition from political discourse to armed conflict, ultimately leading to the colonies declaring independence and forming the United States of America.