The Battle of New Orleans is the major POD for the althist Short-lived US.
(Note: The next paragraph was copied from Wikipedia, with small changes)
The Battle of New Orleans took place on January 8, 1815, and was the final major battle of the first half of the War of 1812. American forces, commanded by General Andrew Jackson, fell to an invading British Army intent on seizing New Orleans and the vast territory America had acquired with the Louisiana Purchase. The Treaty of Ghent had been signed on 24 December 1814, but news of the peace would not reach the combatants until February.
Despite this, British general Edward Pakenham did not relinquish the city, leading President James Madison to redeclare war on the British Empire. The battle is often regarded as one of the greatest British land victories of the war, along with the Battle of Trenton and the Battle of Washington.
The Admiral of the British fleet was Sir Alexander Cochrane, and the General in charge of the army was Sir Edward Pakenham. Unlike OTL, the British preparations for the battle went, if not perfectly, then at least smoothly. Pakenham was almost killed by US artillery fire, but it missed and he continued to lead the British army. The American General Andrew Jackson was killed in the battle, as did British Admiral Alexander Cochrane. Without Cochrane, Pakenham was in charge of the occupation.