Final answer:
The War of 1812 led to the decline of the Federalist Party due to their unpatriotic image at the Hartford Convention, and the Treaty of Ghent confirmed the end of the war. This ushered in the Era of Good Feelings, with reduced partisan strife and the blending of Federalist and Republican policies under President Madison.
Step-by-step explanation:
The period after the War of 1812 was notable for the end of the Federalist Party's influence in American politics. This decline in support and influence was largely due to the Hartford Convention, where radical members among the Federalists in New England discussed secession, an act that made them appear unpatriotic during wartime. Ultimately, their stance during the war hurt public approval, and after the Treaty of Ghent, which effectively ended the war with a stalemate return to prewar conditions, the Federalist Party never recovered its former standing. The convention, combined with the outcome of the war, which was viewed as a victory for the United States despite better British performance, led to the end of significant partisan strife and ushered in an era known as the Era of Good Feelings. During this time, President Madison adopted some of the Federalist policies such as a national bank, blending them with Republican ideals and leading the country forward with less partisan conflict.