In June 1812, President James Madison sent a message to Congress detailing American grievances against Great Britain, although he did not explicitly call for a declaration of war. After four days of deliberation, the House of Representatives voted in favor of a war declaration with a close margin, marking the first time the United States had declared war on another nation. The conflict centered on maritime issues, particularly British blockades. Federalists strongly opposed the war, and it was dubbed "Mr. Madison's War."

Meanwhile, Prime Minister Spencer Perceval's assassination in London on May 11 led to a change in British leadership, with Lord Liverpool coming to power. He sought a more practical relationship with the United States and, on June 23, issued a repeal of the Orders in Council. However, communication in those times was slow, and it took weeks for this news to cross the Atlantic. On June 28, 1812, HMS Colibri was dispatched from Halifax to New York under a flag of truce, carrying a copy of the declaration of war, British ambassador Augustus Foster, and consul Colonel Thomas Henry Barclay. It took even longer for the news of the declaration to reach London.

In the midst of these developments, British commander Isaac Brock in Upper Canada received news of the war declaration promptly. He issued a proclamation urging vigilance among citizens and military personnel to prevent communication with the enemy. He also ordered offensive operations against American forces in northern Michigan, who were unaware of their own government's declaration of war. The Siege of Fort Mackinac on July 17, 1812, became the first major land engagement of the war and ended in a decisive British victory.