Warning: SPOILERS for Star Trek: Discovery season 3, episode 3, "People of Earth"
Star Trek: Discovery's latest episode revealed that Earth is no longer a part of the Federation in the 32nd century, causing them to revert back to an era similar to that of Star Trek: Enterprise. Enterprise, which ran from 2001 to 2005, was a prequel to Star Trek: The Original Series and explored the adventures of the very first Starship Enterprise under the command of Captain Jonathan Archer. It was something of a departure from the rest of the Star Trek franchise, focused on a time when the United Federation of Planets did not exist yet. During its four-year run, the show depicted how the Federation was conceived, with the final episode culminating in the founding ceremony for the organization.
Star Trek: Discovery season 3 is also set in a time without Federation oversight. Discovery traveled to the 32nd century at the end of season 2, only to find that Starfleet and the Federation had been devastated by a mysterious event called The Burn, during which most of the dilithium in the galaxy became inert, causing widespread destruction. Searching for answers, the crew takes their ship to Earth in episode 3, only to be greeted with a cold welcome. Since The Burn, Earth has become isolationist to the point of hostility. Discovery is intercepted by Captain Ndoye of the United Earth Defense Force, who reluctantly explains what has happened to Earth.
According to Captain Ndoye, most of the ships destroyed in The Burn were Federation, and no one was sure if what had happened was a targetted attack on the organization. The Federation posed a potential threat to Earth if The Burn ended up being just the beginning of more attacks, so they left. Ndoye reveals that the Federation and Starfleet have not been on earth for 100 years in an effort to keep the planet safe. Whether or not the Federation agreed to leave or was forced to by those who saw it as a threat is not explicitly stated, but from Ndoye's attitude, it is clear that most of those currently living on Earth have no interest in being part of the Federation. Earth has rebuilt itself after The Burn, but has come under heavy attack from raiders looking to steal any remaining dilithium and other resources. Ndoye makes it clear that Earth has continually had to fight for anything they've had since The Burn.
With the Federation missing, and Earth no longer a part of it, the planet has essentially become how it was before the Federation existed: a self-governing, self-sustaining, and vaguely isolationist body. This is reminiscent of how Earth was during the Enterprise era, and the hostility displayed by the United Earth Defense Force could be indicative of xenophobic sentiment among Earth's population, perhaps similar to the Terra Prime movement, a group depicted in the final season of Enterprise that sought to remove non-human races from Earth and retain human supremacy on the planet.
Star Trek: Discovery and Star Trek: Enterprise have always had some correlation with each other. Like Enterprise, the first two seasons of Discovery were a prequel to TOS. Now with The Burn, Discovery has found itself in a galaxy that looks a lot like the galaxy Enterprise's crew explored. Ultimately, it seems as though season 3 of Discovery will have to answer some of the same questions Enterprise did, but whereas Enterprise grappled with the birth of the Federation, Star Trek: Discovery will have to grapple with the more daunting task of how to rebuild it, and hopefully return Earth to its place as Starfleet's galactic seat.