It was once considered "manifest destiny" that Minneapolis and St. Paul would become one city. A conjoined municipality would have a population similar to Seattle and Denver. But this idea never took off, despite simmering in the public discourse for many decades.
The Star Tribune's Kevin Duchschere wrote a Curious Minnesota story on this topic. He joined Curious Minnesota podcast host Eric Roper to discuss why the central cities of the Twin Cities region remained separate.
Why didn't Minneapolis and St. Paul ever merge? (March 2023 Curious Minnesota article)