The Toledo War of 1835-36.
The state of Michigan and the state of Ohio almost entered into armed conflict over the ownership of Toledo. The US Government settled the dispute by giving Toledo to Ohio and the Upper Peninsula to Michigan.

Leaving Wisconsin to say "What the what? We weren't even in this mess!". The Upper Peninsula is connected by land to northern Wisconsin, but is only reachable from mainland Michigan by boat or driving over the Mackinac Bridge.

Of course Michigan, Ohio State, and Wisconsin all have football teams in the Big 10. And Michigan / Ohio State is one of the most fierce rivalries in college sports. Coincidence?