After the American declaration of war, Brigadier-General William Hull led a force of 2,500 troops to Fort Detroit. Once he had reached the fort, the American force was to cross the Detroit River and capture Amherstburg. British Major-General Isaac Brock rushed to the threatened town from York (Toronto). He arrived with 50 regulars and 250 militia on 13 August 1812.
The Shawnee leader, Tecumseh, was already encamped outside Amherstburg with 500 warriors from the Shawnee Confederacy when Major-General Brock arrived. Combined with the garrison at Amherstburg, Tecumseh and Brock had a force of 1,100 men, including 300 British regulars of the 41st Regiment and 400 militia. Despite being outnumbered two to one, Major-General Brock decided to attack Fort Detroit.
On the morning of 16 August, Brock's combined force crossed the Detroit River and advanced on the American fort. He dispatched an emissary under a flag of truce to demand the surrender of Fort Detroit. In his message, he expressed concern that he may not be able to control the Native warriors and informed Brigadier-General Hull that a massacre might occur. The American commander, well aware of Native hostility toward the Americans, agreed to surrender. That afternoon, British troops entered Fort Detroit, and detachments of British regulars and militia marched the American prisoners to York.