The MCU has been built around "phases," each one ending with a different "Avengers" movie, and it has all led to next year's "Avengers 4," which is a concluding chapter in this era of the MCU.
Going forward, Marvel will likely use new characters to build up to different events, similar to "Infinity War." It's also loosely adapted events/storylines from the comics and scaled them down, such as "Civil War" ("Captain America: Civil War") and "Planet Hulk" ("Thor: Ragnarok").
"Annihilation" is a 2006 Marvel Comics event about a war involving Marvel's space-based characters, including Guardians of the Galaxy, Nova, Silver Surfer, Galactus, and the shape-shifting alien Skrulls.
The Nova Corps, a galactic police force, was already introduced in the MCU in "Guardians of the Galaxy" and were said to be wiped out by Thanos in "Infinity War." But that sets up Nova's origin story as the final Nova Corps officer.
The Skrulls will likely be introduced in "Captain Marvel" next year.
With Fox-owned characters like Surfer and Galactus, the MCU could build up to an event similar to "Annihilation."