The arrival of Michael Burnham in 3188, followed by the USS Discovery a year later, in a galaxy shattered by the Burn.
To keep the sentient Sphere data out of the hands of the rogue AI Control, Michael Burnham led the USS Discovery through a wormhole far into the future. Burnham came out first, in 3188, and crashed into the ship of the courier Cleveland Booker. From him she learned that the Burn had destroyed most of the galaxy's dilithium and with it much of Starfleet.
The Federation she knew had broken apart. Burnham found Aditya Sahil, a lone Federation liaison who had kept watch at an abandoned station for decades in the hope that a Starfleet officer would return. She gave him an acting commission, then spent a year searching for her ship.
Discovery arrived about a year after Burnham, in 3189. Once reunited, the crew found the hidden Federation Headquarters and Admiral Charles Vance, and their ship was refitted with 32nd-century technology. Its spore drive, which needed no dilithium, made Discovery one of the most valuable ships left in the Federation.