This question already has an answer here:
AFAIK, the United Federation of Planets and Starfleet both have their headquarters on Earth and it is somewhat implied to be where it all started. I'm not sure about that second point -- there's probably some canon about the creation of the Federation that I'm not familiar with -- but the "lay impression" given is that it is very much human/Earth-centric.
It seems hard to believe that a bunch of other races would unite with the upstart humans, once they discovered warp technology. It's even harder to believe that said races didn't have the collective wherewithal to have formed a political union already, letting Earth join once it had reached a certain "maturity".
Is there an in-universe reason for the Earth-centricity (presuming that's the case, of course)?