The politics of the United States were not always the nice and amicable affairs that they are today. Occasionally disputes would arise when it came to drawing up the borders of the different states. Drawing up the Michigan-Ohio border was no exception. The bone of contention was what was known as the Toldeo strip.
The different intrepretations of this border created what was known as the Toledo Strip. This was a chunk of land contested by Michigan and Ohio. Ohio started to settle more of it and this angered the Michgiganders. In 1835, the Michigan governor made it illegal for Ohioans to settle in this strip of land. Militias were formed by each state and they came to battle.
The rivalry has migrated from open warfare (or bar brawls) to the Michigan-Ohio State game.