What was the largest battle of the American Revolution?

The Battle of Long Island, the first major battle of the war, took place on August 27, 1776 in Kings County, the current NYC borough of Brooklyn.

George Washington, with approximately 10,000 troops, faced 20,000 British troops. Earlier forced out of Boston in 1775, and repulsed at Charleston, the British had no major base in the American Colonies. A slow build up of British naval and military forces in New York harbor gave the Americans plenty of time to respond, but they were no match for the professional British army which included German soldiers, "Hessians", who were forced by their rulers to fight as mercenaries.

This was the greatest concentration of troops during the war. Learning from their foolhardy tactics at Bunker Hill, where they advanced over open ground against a prepared position, the British easily surprised and outflanked the Americans. The Americans were routed on the battlefield , part of which is now Prospect Park. Americans who tried to surrender were bayoneted by the Hessians. The British suffered a total of 388 casualties against over 2,000 for the Americans.

The British captured New York, which remained in their hands for the reminder of the war. Washington's army was chased for several months and faced several more defeats. However, in defeat, Washington proved brilliant. He escaped time and time again, keeping the army intact. The Revolution remained alive, as long as Washington's army existed. Ultimate victory came to the Americans in 1783.