A Fourth of July thought experiment
The Fourth of July—a time we Americans set aside to celebrate our independence and mark the war we waged to achieve it, along with the battles that followed. There was the War of 1812, the War of 1833, the First Ohio-Virginia War, the Three States' War, the First Black Insurrection, the Great War, the Second Black Insurrection, the Atlantic War, the Florida Intervention.
Confused? These are actually conflicts invented for the novel The Disunited States of America by Harry Turtledove, a prolific (and sometimes-pseudonymous) author of alternate histories with a Ph.D. in Byzantine history. The book is set in the 2090s in an alternate United States that is far from united. In fact, the states, having failed to ratify a constitution following the American Revolution, are separate countries that oscillate between cooperating and warring with one another, as in Europe.