Worlds of Magic: Planar Conquest (EP)

There are 7 Diplomacy states: Peace, Truce, Non-Aggression Pact, Defensive Alliance, Alliance, War, and Eternal War. Once any opponent enters into Eternal War they will never change. This trophy requires you to successfully enter into an Alliance state with any opponent Sorcerer Lord.

Unfortunately I do not have a solid way to unlock this trophy. You cannot just make an alliance with anyone that you want and the way that this occurs is a mystery to me.

There is a Tier IV Mentalism spell named Aura of Majesty. This spell states that it improves the relations with other Sorcerer Lords. I do not know the affect of this spell on the AI offering you an Alliance, but I do recommend using it if you can get it. When I personally unlocked this trophy, I was not using it so I can confirm that it is possible to get the trophy without it.

I created a large enough map where I was able to start a game against 8 computer opponents. I chose Tier IX in Earth with 1 point in Summoning then sat in my starting city round after round researching higher and higher summoning spells. I did upgrade my town a decent amount but I literally never left. I also turned off Auto-Save and just manually saved whenever things seemed to be going OK. I went through turns as fast as I could while learning spells (this was just in case I was attacked).

I accepted every single Trade offer that any computer sent at me. There were quite a few in the first 100 turns. Eventually some of the opponents starting declaring War on me. After two of those, the next opponent initiated an offer of Alliance with me. Accepting caused the trophy to unlock immediately. This only took me about 20 minutes.