The Forgotten War isn't even confirmed to be real. It hasn't been confirmed not, either. It's a guess. There is zero evidence of there being a war in this era since IM STILL ALIVE (Ilovecreepypasta for this time) wasn't there for it. She was gone from Wikia and there are zero recordings of it even existing.
This war, if real, would take place after IM STILL ALIVE was banned from her Ilovecreepypasta account. The war would have wiped out whatever remaining Venkons there were left. If so, it would be a manipulation method. The Ivichs would have used each users fear to their best extent to form a weapon.
It's hard to tell if it was a verbal war over physical to the remaining users. It could have even been split. After she had come back, no users were able to be contacted. Most had their accounts missing, shut down, or just unresponsive. Some came back, but very few compared to what there was.
Maybe, just maybe, there was never a war after she went missing. It could have been that her absence scared everyone and they left for their own safety. But who's around anymore to tell what happened anyway?