User blog comment:JakePT/Mass Effect 3 to be Revealed at VGA Awards?/@comment-216.40.154.60-20101130050458/@comment-217683-20101201050536

But Cerberus couldn't have started the war, at least not if this is a war that occurred before the First Contact War. There's that whole pesky "Cerberus not existing before the First Contact War" thing. At least, if we go by the latest info we have on Cerberus. We know that they most likely didn't exist before the First Contact War, and that if they did, they certainly didn't exist before the Alliance did. And we know that no major wars other than the First Contact War occurred- post-creation of the Alliance.

So no, we can reasonably say Cerberus didn't start or instigate any wars before it existed.