The event that marked the beginning of the American Revolutionary War was the Battles of Lexington and Concord, which took place on April 19, 1775. These skirmishes were the first military engagements between the American colonists and British troops. Tensions had escalated due to British taxation and regulation without colonial representation, leading to increased animosity. The phrase "the shot heard 'round the world" is often used to describe the significance of this conflict, signaling the start of the colonies' struggle for independence and establishing a revolutionary spirit that would lead to the formation of the United States.