The British returned in force in August 1776, landing in New York and engaging the fledgling Continental Army at the Battle of Brooklyn in one of the largest engagements of the war. They eventually seized New York City and nearly captured General Washington. The British made the city their main political and military base of operations in North America, holding it until 1783, when they relinquished it under the terms of the Treaty of Paris. Patriot evacuation and British military occupation made the city the destination for Loyalist refugees, and a focal point of Washington's intelligence network. The British also took New Jersey, but in a surprise attack, Washington crossed the Delaware into New Jersey and defeated British armies at Trenton and Princeton, thereby regaining New Jersey. While the victories involved small numbers, they gave an important boost to pro-independence supporters at a time when morale was flagging, and have become iconic images of the war. In 1777, as part of a grand strategy to end the war, the British launched two uncoordinated attacks. The army based in New York City defeated Washington and captured the rebel capital at Philadelphia. Simultaneously a second army invaded from Canada with the goal of cutting off New England. It was trapped and captured during the Battle of Saratoga, New York, in October 1777. The British army had agreed to surrender only on condition of being a Convention Army with repatriation to Britain. Realizing that their cause would be adversely affected if the captured troops could be switched with other British troops who would be brought out to America, Congress repudiated these terms, and imprisoned them instead. This was poorly received in Britain, as a violation of the rules of war, and contributed further to the drift apart.