On June 18, 1812, President James Madison signed the declaration of war passed by Congress on June 17, 1812, starting the War of 1812. I think it is safe to say that rarely has the United States gone to war more ill-prepared than in 1812, with an Army of 7,000 men and a Navy with 12 combat vessels, which is odd considering that there was no precipitating crisis that mandated a declaration of war at the time. The United States could have prepared for the conflict and then declared war, but no such pre-war preparation occurred.
The vote totals in Congress, in the House 79-49 and in the Senate 19-13, indicated that the war was largely at the desire of one political party, the Jeffersonian Republicans, and opposed by the Federalists. The opposition of the Federalists would continue throughout the war, and the conflict would be bitterly divisive in the United States.
The whole undertaking has a fairly surreal quality in retrospect, with the Madison administration, propelled by the War Hawks in Congress, undertaking a war that the President himself thought unwise and ill-considered against the mightiest Empire in the world.