The Upper Peninsula of Michigan—also known as Upper Michigan or colloquially the U.P.—is the northern and more elevated of the two major landmasses that make up the U.S. state of Michigan; it is separated from the Lower Peninsula by the Straits of Mackinac. It is bounded primarily by Lake Superior to the north, separated from the Canadian province of Ontario at the east end by the St. Marys River, and flanked by Lake Huron and Lake Michigan along much of its south. Although the peninsula extends as a geographic feature into the state of Wisconsin, the state boundary follows the Montreal and Menominee rivers and a line connecting them.

The Toledo War (1835–36), also known as the Michigan–Ohio War or the Ohio–Michigan War, was a boundary dispute between the U.S. state of Ohio and the adjoining territory of Michigan over what is now known as the Toledo Strip. Control of the mouth of the Maumee River and the inland shipping opportunities it represented, and the good farmland to the west were seen by both parties as valuable economic assets.