Note: This is all my speculation, if you disagree, make your own speculation blog
So, let us for a moment assume that SK never plotted to hit Rose after this war, and that SK never hit Vanguard.
In this universe, SK and Guardian both declare on VE first, just like what happened here, only that SK never hits Vanguard.
VE, then naturally calls on their allies, BK, WWF, tS and Cornerstone, and they both declare war on Guardian and SK.
The war then expands, as Guardian calls on Vangu