Yeah, and the game models long-standing alliances by building Trust between nations. The AI will remember if you renege on alliances or pull other shady things, like exiting out of wars independently before they sign the peace treaty.
Here’s a simple example of their diplomacy systems at work: You can designate provinces around you as being of “strategic interest” (a Claim on a province automatically makes it so). The cool thing is, this means that if the AI is the war leader and is negotiating peace, they will know to carve off a slice of the pie for you, because you desire those provinces. However, it will only do so if they also don’t consider those provinces to be of strategic interest. In fact, the AI will do it’s best to not call you into their wars of aggression if you’re competing over the same territory. They know that if they call you in, you will want territory and try to grab some for yourself.
In a game as the Netherlands, I had a long-standing alliance with France that lasted a couple centuries. Spain had inherited the Lowlands, and France and I had spent a couple generations beating them up and carving up the spoils between us. However, once they were driven back to Iberia I got a popup warning that I had an Alliance that was about to break. Hovering over the tooltip, I could see that France valued our alliance strongly due to how long it lasted and how much Trust I had built over the years. However, that was being outweighed because we both had 6-8 highly valuable provinces listed as being strategically important to us. France AI was making a calculation that, with Spain subdued and both of us wanting the same land, I was looking more like a competitor than an ally.
So, I went into the diplomacy screen and reduced the strategically important provinces to those that I really cared about, rather than just carpeting the whole region as important. The alliance was saved and France and I continued to be best buds for another good 60-70 years, before we started getting into tangles over colonial territory and we mutually parted ways.
When I see Triumph talking about these diplo systems in Planetfall, that’s what makes me hopeful. They have working models of diplomacy that they can go off of. Now, I don’t expect Planetfall to be EU4-level of diplomacy, but if they can get some of those basic mechanics down (which it sounds like they are with cassus bellis and things like that), that would be a huge step up in the 4X space.