An example slightly to the contrary, and pardon the use of past strats as examples, is the Chaos/Druzhina alliance in strat 2. It was an official and public alliance. We were friends, too, to an extent, but not to the point where we'd stay that way forever. We never talked much after the NA side got split from the EU side in later strats. Now here's where the example comes into play: Chaos members were also for a long time very close friends with the members of the FCC. It was personal. We had always wanted to work together with FCC on Strat, but circumstances kept us apart. The end of this scenario was when our ally Druzhina was declaring war on our friend FCC. Diplomatically, we were bound to Druzhina. We decided, in the spirit of the game, to go along with them and fight with our allies against our friends. I don't think some of them ever forgave us for it. I still feel as though there's a grudge harbored somewhere in there to this day... but would it have been better if we'd broken our alliance with Druzhina before it played out just because we didn't want to hurt the feelings of someone we liked?
I wanted to get this off my chest because I've seen you posting about it a few times and heard it over that audio file that Rhalzo posted.
As far as your claim of the FCC having a grudge I do not know about them, but I still hold a grudge for two active members in your faction that I don't think I can ever let go and it has nothing to do with the FCC being attacked. I embraced that conflict with open arms and wore my try-hard pants to do the best I could against you guys.
The Unicorns (Bramd, Governor, Elyze, Kilgore, and I) really disliked the image of your clan because of the way we were treated/talked to by a few members of Chaos while we were still independent and trying to learn the game, no need to throw out names but I'm sure one of them is obvious. Pretty much after the Rebache battle we were treated better by most of those people that we felt disrespected by and my bitterness for your clan went away, which I'm happy for because I've now made a lot of battle buddies/friends with the current and ex members.
I also get the impression you personally harbor a grudge too.