Final answer:
The cause of Americans defeating the British in about two hours was due to American guerrilla tactics, British overconfidence, and a key victory at Breed's Hill, which was misidentified as Bunker Hill. Even though the British won the battle, it was a pyrrhic victory that later contributed to the increasing American morale and eventual triumph with French alliance.
Step-by-step explanation:
The cause of the American forces defeating the British in a short amount of time can be traced back to several key factors. One monumental British mistake was the belief by Major General Sir William Howe that taking the hill would be simple, leading to a direct assault during the Battle of Bunker Hill (misnamed, as the primary combat took place on Breed's Hill). Though outnumbered, with 2,400 American troops facing 3,000 British forces, the Americans utilized guerrilla tactics, firing from behind cover and inflicting significant British casualties. Although the British technically won, their victory was pyrrhic, with 226 soldiers killed and over 800 wounded, shaking British confidence. This battle also set the stage for the eventual American victory, aided by a diplomatic alliance with France and naval victories that boosted American morale, such as the USS Constitution's evasion of British pursuit.