The American Revolution began as protests against new taxes imposed by the British government on the American colonies, including the Stamp Act of 1765 and Townshend Acts of 1767. Tensions escalated throughout the 1770s as the British passed more punitive laws in response to colonial unrest, such as the Intolerable Acts in 1774. Open conflict broke out in 1775 with the Battles of Lexington and Concord, marking the unofficial start of the Revolutionary War. In 1776, the Second Continental Congress declared independence from Britain and the colonies united as the United States of America.