If you really want to gimp the United States, you could also have had the US lose the equivalent of the War of 1812 and the creation of a Native American confederacy in the modern Midwest. Manifest Destiny would never have happened, and a big portion of the cotton belt would be denied to the Southern plantation system. The US not getting Louisiana (and with it control of both banks of the Mississippi) would be huge. It would make a very interesting Western Hemisphere if Napoleon had worked with L’Overture instead of launching a disastrous invasion.
Suggestion: have one of your hinge points for the alternate history be about Haiti, L’Oveture, and Louisiana.
