Milwaukee's location at the confluence of three rivers – the Milwaukee, Menomonee and Kinnickinnic – provided natural boundaries for the original three founders. Shrewd businessman Byron Kilbourn established Kilbourntown on the west side of the Milwaukee River; former fur trader Solomon Juneau established Juneautown east of the Milwaukee River; and George Walker established a trading post south of the Milwaukee River in what later became the 5th Ward, or Walker's Point.

The early settlers of each community had strong partisan feelings and engaged in fierce competition to keep their settlements separate. Juneau and Kilbourn even built street grids that intentionally did not line up. (To this day some of Milwaukee's downtown bridges are on a diagonal, often posing visibility issues for boaters.)

On May 8, 1845, angry West Siders destroyed the west side of the Juneau Avenue Bridge and damaged the west side of the Wells Street Bridge, touching off what is known as the "Bridge Wars." East Siders retaliated with the destruction of the Wisconsin Avenue Bridge and threats to destroy the dam across the Milwaukee River. Armed brawls broke out between the inhabitants of the two towns, resulting in several serious injuries.

The Bridge War ended in a truce, but tensions remained until January 31, 1846, when the legislature passed a charter establishing a unified City of Milwaukee.