If the Federation has so many races, why is Starfleet filled with humans?
Let’s go back to what the Federation is. It’s not the United States in space. It’s the United Nations in space.
Starfleet is based out of San Francisco, the origin of the United Nations, and the Federation flag is the UN flag with a darker shade of blue and the stars instead of earth.
Like the UN, the Federation is not a government. It’s a forum. It has members not states. Its military force depends on contributions. When there’s a real shooting war that the UN gets into, the big muscle comes from the US. Humans are the Americans of the Federation. They’re mean enough to be dangerous, but not mean enough that other races are threatened by them. They’re altruistic enough to help out without losing their military edge. And they’re also curious enough to be explorers. And most of all, they’re willing to foot the bill to play explorer and soldier.
Starfleet is filled with humans because they’re the ones that spend the money, put up the manpower and take the risks.
Logically, an organization like Starfleet is going to appeal to races that colonize a lot of planets. A species that just has to defend its own home system is not going to need to do much exploration or need a wide defense net.
A species with three systems and no drive to settle new worlds is not going to put in the energy and lives to run something like Starfleet. Humans aren’t the only species to settle new worlds, but they’re the most aggressive settlers in the Federation. Having an organization like Starfleet to find new worlds and protect farflung colonies served their needs.
And once it got going, Starfleet was institutionally defined by humans. If you’re an aggressive species that isn’t interested in exploration, Starfleet isn’t going to be a great fit for you. See Worf. If you’re a peaceful race that values exploration but not conquest, it won’t be a good fit either. There are Vulcans in Starfleet, but they don’t like it.
Starfleet has a human balance of exploration, defense and diplomacy. Other species have to adapt to it.
The Federation Council theoretically sets the agenda, but Starfleet has its own institutional culture and its captains make snap decisions that change history.
Starfleet lets humans do some of the same things as the Klingons and the Romulans, but without the ugly side. The Federation gives humanity the blunt force and power of an empire without having to conquer other races. Instead members get rewards and access to an interstellar network. It appeals most to smaller and weaker races. Or races that don’t like fighting.
The Klingons would never fit well into the Federation. A large species that can match humans in aggressiveness and expansionism would make for a tug of war. But a species like that wouldn’t join.
A Federation composed of a lot of smaller and weaker races is never going to displace humans in Starfleet. And it would be difficult to displace humans without changing what Starfleet is. Non-humans can preside over the Federation Council, but to wield any force, they need Starfleet. And Starfleet keeps the Federation together. It’s a huge asset to a small world to be able to call on a force that can stand up to any fleet in the neighborhood.
And since humans want to run it anyway, everyone lets them. It’s either that or work out how dozens of smaller alien races can build a new institutional culture for Starfleet together. That might be more IDIC, but it would be chaos.
The Federation lets humans have an empire without the imperialism. On their own, humans could have learned to match the Klingons or the Romulans, but they would always be just another race. The Federation gave them a technological boost and a network of different worlds to join without conquering. And Starfleet links that technology to military applications that races like the Vulcans are uncomfortable with.
It’s an arrangement that works.