I mean, this could be okay if its about Shepard trying to unfuck the galaxy right after the Reapers are vanquished and all the old grudges start flaring back up. Big threat defeated, but why rebuild when you can take from your nemeses? The Council races almost certainly hate mankind over Udina and Cerberus, and someone was left unhappy as all fuck thanks to the genophage arc, either the Salarians or the Turians, and you've got the krogans back with their population starting to recover (aided by genophage or even not since they probably made out the best compared to everyone else due to their smaller numbers) and everyone else devastated by the Reapers. Don't introduce a threat, don't hint at a threat, just make it galactic politics, and Shepard, as one of the few living Spectres and hero of the Reaper Invasion, has to try and make sure things don't completely fall apart in the aftermath as everyone starts threatening full-scale war.
