Not to pick on anyone especially not picking on my friend flutterby, but this whole coming to a "mutually beneficial agreement" as some sort of evidence for a fake war is just a fallacy. If I write to someone and say, "Hey I have a proposal that is mutually benefitting". and they write back and say "ohh yeah what is that?" and I write again and say, "I suggest we have a war?" and they could ask (like everyone else might ask) "how is that "mutually beneficial"", I would answer by saying, "Wars are fun and if we war, we might both have fun, and I find that mutually beneficial!"
TLDR: Because Wars are fun, they are "mutually beneficial"!