Comedy is largely based in reacting. And most comedy theaters (in Chicago anyway) were founded as reactions to other theaters. This is a gross oversimplification, but let's go with it anyway...

Second City grew out of the Compass Players which was founded as an attempt to put up shows differently than traditional theater. Second City's very name is a self-deprecating joke about not being New York City.

Eventually Del Close left Second City over an argument about whether improv was best used as a tool to generate scripted material or if it could be entertainment in and of itself. Del Close thought it could be, and he and Charna Halpern founded the Improv Olympic, which set itself apart from Second City by doing improv for improv's sake.

Second City and Improv Olympic made a lot of money teaching the rules of improv, and the founding philosophy of the Annoyance Theater was partly a reaction to feeling too restricted by those rules.

The Playground, a "not-for-profit co-op theater," was founded as a reaction to players and teams not having enough say in the running of the theaters where they performed.

There are other improv theaters in Chicago, but off the top of my head I can't think of how they'd support my flimsy thesis, so I'll just ignore them.

Supposedly there was a time when performs would align themselves with one theater and be adamantly against the others. "I perform HERE! I would never perform THERE!" These days, though, the same people teach, direct and perform at several different theaters. The venn diagram that is Chicago improv includes a lot of overlapping circles.

Sure, you still hear the occasional passive-aggressive dismissal of one of the theaters ("Second City is an out of touch tourist trap"; "iO is like a cliquish high school where all the shows are the same"; "The Annoyance is just dirty for the sake of being dirty"; "The Playground has small audiences"), but the truth is that they each churn out their fair share of brilliance and crap.