Final answer:
The Federalist Party stopped existing after the War of 1812 due to their perceived unpatriotic actions during the conflict.
Step-by-step explanation:
The political party that stopped existing after the War of 1812 because they were viewed as unpatriotic and treasonous was the Federalist Party. The depth of the Federalists' discontent with the power of the slaveholding Virginians led to the December 1814 Hartford Convention, where some attendees even called for New England to secede from the United States. These arguments for disunion during wartime, combined with the convention's condemnation of the government, made Federalists appear unpatriotic and led to the downfall of the party.