My early diplomacy was the usual fair. "yo, 'sup. Let's kill indies. Peace out." My misguided goal early on was trying to make lasting peace with most of my neighbours. These ended up being Caelum and Abysia, by the virtue of seeming more friendly than scary jaguar men or enigmatic and imposing wolf men. And I guess there was Pangaea but he was only neighbouring me buy a rarely freezing river. Didn't feel like a threat.
Some noteworthy transactions were trading most of my D gems (Turmoil-2/Luck-3/Magic-3 nets you a
TON of gems) to Caelum from quite early on. I got some horror helmets from him. I also just did flat out trading or so I recall. I had a ridiculous amount of D gems. I also did some trading with Abysia. Pretty much anything to keep those two guys happy.
I never really talked with Midgård, sure we agreed to a border early and collaborated a bit against Patala but that's largely it. Same is true for Mictlan, he sent a frankly very brutish "stay off my lawn" type message at me early. Not that I was going to argue, those jaguars scared the crap out of me. Anything to placate the monstrosity. "Peace in our time" was the slogan at the time. Incidentally I worked to make a mutual protection pact with both Abysia and Caelum should Mictlan attack me or the other (I negotiated individually with Abysia and Caelum, they didn't hear from me that I was cavorting them both). I was honestly committed to it, but I don't know how my pact mates would have responded if it ever came to be tested. Not that it mattered, it ended with me attacking Mictlan. I expected no support since it was a defensive pact, and I got none (other than Bogarus but I had specifically negotiated with him for war assistance against Mictlan).
It's worth noting that I also discussed with Pangaea before every war I fought. He never really seemed to budge much. Though I seem to recall that I later learned he was some sort of ally/fair weather friend for Mictlan, which would explain some of his reluctance to gang up.
As for the big war to end all wars with Bogarus. I think I started plotting against him some dozens of turns before hostilities actually started. Caelum, Abysia and Pan may remember me sending inviting messages every now and then about purely hypothetical hostilities against Bogarus. As the eventual 3-2 situation proved, it didn't amount to much.
As for other trading, hmm... I think I was selling slaves and W gems to Abysia (or was he selling me W gems in exchange for slaves?). I also sold a bunch of slaves to Bogarus. I did remark at the time how poetically just it would be for me to die to the demons of Rus and Abysia. Funny how that turned out
Likewise I provided D for Caelum and E for Pangaea at some points (Patala's E9 pretender had found some seriously awesome E sites). There was also some item trading between me and Abysia. Boosters, supply gear and the like. We were good neighbours until the fiery devil stabbed me like Brutus did to his Caesar. I still weep for the injustice.
I also did some extensive trading with Bogarus before our official clash. I believe I provided him some rune smashers among other things.
I bought a bunch of blood items from both Rus and Abysia. I had some hilariously decked out mages before my freefall to oblivion.
I was communicating quite extensively with Bogarus from Mictlan's fall to near end of the game. I'm guessing it's that communication that may have kept me from attacking Bogarus as long as I did. It's really that much easier to strike someone you've barely spoken to in-game.