Shepard united the galaxy, was proclaimed its ruler, and established a dynasty of Shepard-born emperors. Prior to the events of Andromeda, wormholes opened up all over the Milky Way. Hostile aliens of unknown origins poured in everywhere and tried to destroy the Citadel. Shepard's last known descendant sacrificed their life to close the wormholes forever. All except one, begin Andromeda. The Asari Dominion is extending its grasp over the universe, claiming that Shepard is not a real god and should not belong to the space magic pantheon. War rages on in Andromeda over the same question...oh and a supreme Reaper got shot forward in time and wants to Reap everything.
...wait, this sounds oddly familiar.