They kept the brits busy in the war of 1812 After peace in 1815 some of the units who fought in the war of 1812 actually went over and fought in waterloo. What if those units got wiped out in the Americas? What if the US didn't accept a peace treaty and fought on, and those units never got a chance to fight in waterloo?
Just because the US didn't directly interact with france doesn't mean they weren't important to how things ultimately played out. There was a rather major war going on in the US, even if it wasn't the focus of world history at the time (ol boney sorta hogged the spotlight, you know?)