Is this a trick question? I'd immediately assume War of 1812 (if you mean "at war against the British", vs. fighting as allies, which would be...today). There

Is this a trick question? I'd immediately assume War of 1812 (if you mean "at war against the British", vs. fighting as allies, which would be...today). There were stirrings during the US Civil War, but it didn't rise to combat.