Relocating to Detroit, 1935
I decided to sprinkle in a few more moves that weren't free-agent or trade related that could have drastically changed the history of the Cardinals. A move to a whole different city qualifies for sure.
In 1934, the Gashouse Gang beat the Detroit Tigers in the World Series. The Cardinals owner at the time, Sam Breadon, was open to moving the Cardinals to a different city, as they were not drawing the same amount of fans as other cities, and had another team, the Browns, in St. Louis already.
Back then, Detroit was a booming sports town and was ready to add another team if given the opportunity. But the Tigers' ownership would have never allowed for it, and the lack of other clear options ended up putting to bed the idea for the Cardinals' owner and they have remained in St. Louis ever since.