'Weird to think the Brigade is any different, really. I still don't know how much is prudent to say, though. Maybe the version for the public?'

Well, it's a pretty long story at this point. But basically Haruhi got to high school looking for something interesting, joined all the school clubs, left them, and decided to start her own. Cue forced conscription of various people that, whether by luck or design, ended up working a lot better than you might have expected. To keep her entertained, anyway.