Posting as top-level answer, although quoting from /u/Velostodon's reply about Chicago

Meanwhile, very little happened in Saint Louis.

That is manifestly not true. In fact, St. Louis made itself a victim of its own success and racism.

St. Louis was a genuinely great city in the 19th century, though it had its problems. Chicago had its Great Fire; in the words of industrialist and Washington University founder Wayman Crow, "No city had suffered greater reverses [than St. Louis] by fire, pestilence, and flood." Chicago hosted the 1860 Republican convention; St. Louis hosted the Democrats in 1876. (Yeah, you know...the end of Reconstruction. That convention.) Chicago held the 1893 World's Fair; St. Louis merited both the Fair and the Olympics in 1904. Although the heavily-Catholic city's upper crust was divided between Protestant/Whig nativists who feared the French and especially Jesuit influence over the city, and, well, the Catholics of first French and later German and Irish, that didn't stop the industrialization and development.

But their jealousy to protect what they had would be the city's undoing.

Here is a map of metro St. Louis (which does not have a cool name like Chicagoland) today. Ignoring the light purple and maroon counties, which are largely rural ("Missourah"), you have St. Charles County in dark blue, St. Louis County divided up geographically-which-is-socioeconomically...and that tiny little almond in orange on the right is St. Louis City.

In the 19th century, basically all of St. Louis' wealth and political power was concentrated in the city. However, city governance was run by the county, which was linked to the state government--both of which, since the Civil War, had tended to favor the interests of rural areas in their decision-making. This did not please the power bloc of St. Louis City.

In 1874, they bludgeoned through elections a referendum to "revisit" the post-Civil War state constitution that awarded judicial and economic decision making for St. Louis City to the county and state. In 1876, the city voted to secede from the county. The boundaries were set exactly how you see them in the map: the little orange almond, and the multicolored county. (In the 19th century, St. Louis County is still mostly rural and St. Charles town is really a separate entity--it was the state capital for a period of time. Today it is unquestionably suburban St. Louis).

This worked well initially--all the money, all the power was in the city.

But permanently restricting its borders ultimately proved a terrible decision.

Already around the turn of the 20th century, rich city residents were finding the new waves of immigration distasteful, seeking more land and large houses of their own, and moving to St. Louis' inner-ring suburbs ("Mid-County" on the map--to today, this is the richest area of metro St. Louis). By the 1930s, nearly all the nice new development in the area was necessarily outside the city limits.

After World War II, of course, St. Louis suffered the same suburbanization as other city with the rise of cars and eventual white flight. Except--the city had undercut its ability to cope by eliminating the chances of annexing addition land. Additionally, the rich residents of Mid-County were unlikely to approve of such a move, since the socio-economic fortunes of the city were declining with rising urban poverty (mostly black, some "white ethnic"--St. Louis is a very neighborhood-y city).

So that takes you basically up to the 20-year limit of this sub: a city locked in its boundaries, continuing to suffer from the legacy of its own pride and the white flight of its ongoing racism.