During the 1760s and 1770s, relations between the Thirteen Colonies and Britain became increasingly strained, primarily because of growing anger against Parliament's repeated attempts to tax American colonists without their consent. The Americans readied their large militias, but were short of gunpowder and artillery. The British assumed falsely that they could easily suppress Patriot resistance. In 1775 the American Revolutionary War began. In 1776 the Patriots expelled all the royal officials and declared the independence of the United States of America. After capturing a British invasion army in 1777, the new nation formed an alliance with France (and in turn Spain aided France), equalizing the military and naval balance and putting Britain at risk of invasion from France. The British army controlled only a handful of coastal cities in the U.S. 1780–1781 was a low point for Britain. Taxes and deficits were high, government corruption was pervasive, and the war in America was entering its sixth year with no apparent end in sight. The Gordon Riots erupted in London during the spring of 1781, in response to increased concessions to Catholics by Parliament. In October 1781 Lord Cornwallis surrendered his army at Yorktown, Virginia. The Treaty of Paris was signed in 1783, formally terminating the war and recognising the independence of the United States. The peace terms were very generous to the new nation, which London hoped correctly would become a major trading partner.