American Revolution (also known as American War of Independence), 1775-83, struggle by which the Thirteen Colonies won independence from Britain. Disputes over taxes, administration and the territorial provisions of the Royal Proclamation of 1763 and the Quebec Act, simmering since the Treaty of Paris, 1763, broke into open war at Lexington, Massachusetts, 18 April 1775. Prominent American colonists signed the Declaration of Independence on 4 July 1776.

An effective propaganda campaign conducted by the Americans succeeded in eliciting some support, particularly in Montréal, where there was some pro-American activity. The French Canadian clergy, seigneurs and leading citizens adopted a policy of support for the British, but most of the common people remained neutral and reluctant to become involved. Bishop Briand issued an episcopal mandate denouncing the rebels and urging the people to more active support, but Governor Sir Guy Carleton (Lord Dorchester) had little success raising the militia.

In September 1775 General Richard Montgomery led American forces northward, seizing Ticonderoga, Crown Point and Fort Cambly. When Fort Saint-Jean capitulated in Oct, Carleton abandoned Montréal and the Americans took possession November 13/14. Meanwhile, General Benedict Arnold managed, despite hardships and desertions, to bring some 700 men via the Kennebec and Chaudière rivers to Québec.

Montgomery joined him in early December with another 300 men and during a snowstorm on 31 December 1775 launched a desperate assault. Arnold and his men penetrated some distance into Lower Town but surrendered under counterattack. Montgomery and his leading officers were killed in their attack from the other side of Lower Town. The remaining Americans kept up their desperate siege through the winter, but were easily routed when the spring thaw brought British reinforcements. They abandoned Montréal May 9.

The failure of the American invasion left bitter memories among Canadians and drove many sympathizers into exile. However, there had been little active support for the Americans: clergy and seigneurs remained staunchly loyal and, after some equivocation, so did the merchants. Most habitants remained determinedly neutral, in defiance of Bishop Briand and Carleton. General John Burgoyne led a British counterinvasion southward via Lake Champlain, but he overextended himself and, in the first great victory for the Americans, he surrendered at Saratoga 17 October 1777.

As in previous conflicts, Nova Scotia remained an uncertain battleground during the Revolution. The provincial Assembly voted addresses of loyalty, but illegal town meetings gave secret support to New England. Nearly every important outpost outside Halifax suffered from American privateering. In 1775 rebels seized Partridge Island in Halifax harbour and they made a futile attack on Fort Cumberland (Fort Beauséjour) in 1776, but by 1779 the British had cleared the Bay of Fundy of privateers.

After a protracted struggle, British forces surrendered in October 1781, and the Treaty of Paris, 1783, formally recognized the United States of America. The failure of the American invasion and the influx of some 40 000 Loyalist refugees into Nova Scotia and Québec determined that the development of the remaining British colonies would differ profoundly from their southern neighbours.