The War of 1812 started with many economic sanctions and violations f maritime rights by the British against the US. Many were in favor of war because of the fight for the rights of sailors and the protection of US shipping, this was more present in western states and territories. The war found little in favor and much of the Congress was absent.
New England especially was against the war, they saw it as a way of silence opposition to the Republicans and as a party project. Federalists feared also that an alliance with France would bring the US to the arms of Napoleon, some even called “the touch of France the embrace of death”. Another argument was the fear for the nation, a high-cost venture.