Originally Posted by NCC-73515
Why would Vulcan, Andoria, Tellar and Alpha Centauri give up their fleets and let Earth's Starfleet handle everything?
I doubt that's the case.
In my mind, the Federation absorbed all the interstellar military/exploration services from its member planets (Starfleet, the Vulcan High Command, the Andorian Imperial Guard, et cetera
), leaving each with its own planetary defence force (the UESN [United Earth Space Navy], whose medics served on mostly-human starships such as the U.S.S. Enterprise
as late as the mid-2200s, for instance). The name and insignia of Starfleet seems to have been a relatively natural choice for the fledgling UFP, as it was clearly the most generically-named of all the service fleets in 2161 and was already in use with signage, branding, rank-and-file structure, et cetera