Final answer:
The A. Hartford Convention and its perceived unpatriotic stance during the War of 1812, especially after the victory at the Battle of New Orleans, led to the downfall of the Federalist Party.
Step-by-step explanation:
The fall of the Federalist Party was influenced by multiple events, but the turning point was the A. Hartford Convention. The War of 1812 had been especially unpopular in New England, the Federalist stronghold, because it harmed the regional economy, which was heavily reliant on maritime commerce.
Federalists at the Hartford Convention expressed deep discontent with the Virginia-dominated government and some even suggested the secession of New England from the United States.
The timing of the convention was unfortunate because it coincided with Andrew Jackson's victory at the Battle of New Orleans.
As news of the victory spread, the Hartford Convention's appearance of disloyalty towards the United States government made the Federalist Party seem unpatriotic, leading to its eventual downfall.