When Shepard and the fleets of the rest of the galaxy came through the Sol relay and went on the offensive?
Looking back at some of the cut scene's the scale of the war was shown really well with a co-ordinated effort from all the species fighting together on Earth.
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No, probably not. The Reapers at that point had been doing this for quite some time. They've probably seen their fair share of team-ups. I think they were just annoyed because it would be a more stressful than usual extermination.