Diplomacy is different from other board games which are aced by AI in the past. AlphaGo for example is purely based on strategic reasoning and there are clear set of analytical rules which can be easily modeled into a computer program.
Diplomacy on the other hand involves dialogue, it need to understand the human dialogue, interact with them, predict their moves and craft a plan.
Uses AI models for strategic reasoning and natural language processing.
Meta’s calls this natural language ability “Controllable dialogue model”.