Final answer:
General Howe was winning the Battle of Long Island before he halted his attack, mistakenly believing Washington would surrender. This decision enabled Washington's strategic retreat and continued resistance in the Revolutionary War.
Step-by-step explanation:
The battle General Howe was winning handily before he stopped the attack was the Battle of Long Island on August 27, 1776. Despite his significant victory, Howe made the critical decision to not press the attack against Washington's forces, assuming they would surrender. This decision allowed General Washington to execute a strategic retreat, preserving his army for future battles. Howe's assumption that Washington would surrender without further confrontation was misplaced, and this allowed Washington to evade capture and continue the fight, significantly impacting the course of the American Revolutionary War.