General William Howe's 20,000 British and Hessian troops outflanked and overwhelmed Washington's forces on the Heights of Guan in Brooklyn, inflicting roughly 2,000 American casualties against fewer than 400 British. Washington's subsequent nighttime evacuation across the East River saved the Continental Army from annihilation and allowed the revolution to continue.
It was the first major battle since the Declaration of Independence, and it very nearly ended the war before it began. Washington had split his forces to defend Brooklyn Heights, but Howe executed a brilliant flanking maneuver through the poorly guarded Jamaica Pass, catching the Americans between converging British columns.
American units, including the Maryland 400, fought desperate rearguard actions that bought time for the rest of the army to retreat, suffering catastrophic losses in the process; their stand is still memorialized in Brooklyn's Prospect Park area. By evening, Washington's remaining forces were pinned against the East River with the British seemingly poised to finish them off.
What saved the Continental Army was Howe's caution and, two nights later, an extraordinary and audacious evacuation: Washington ferried roughly 9,000 troops across the East River to Manhattan under cover of darkness and a fortuitous fog, without losing a single soldier, in one of the most consequential retreats in military history.