Though no one event caused the American Revolution, the war began as a disagreement between the Americans over how the British treated them. Americans wanted the rights that all Englishmen had, such as representation, while the British felt the colonies belonged to the crown and didn't deserve rights.
The road to revolution began in the wake of the French and Indian War when the British government decided that the American colonies should pay part of the costs associated with the war and added taxes to common goods, such as sugar, molasses and tea. Colonists disagreed, suggesting that they deserved to have representation in Parliament if they were to shoulder some of the war costs.
The passage of a tea tax in 1773 resulted in the first revolutionary act, when colonists in Boston boarded merchant ships and tossed their cargo and tea overboard. In response, the British Parliament passed the Intolerable Acts, closed Boston Harbor and sent in troops to occupy Boston. The Colonial militia met the British troops in Lexington, and the war began. While the Colonials won that skirmish and managed to push back the British, the war lasted from 1775 to 1783.
Historians estimate that one-third of colonists supported the American Revolution, one-third sided with the British and one-third remained neutral about breaking away from British rule.