Sorry, my "mistake", I've taken over Pan for a few turns (haven't heard from OG, and I've never played Pan before either so was giving it a whirl), but I should have turned it AI last turn. Because I didn't check for existing NAPs or alliances first, I just played like a "Human AI opponent", figuring everybody around me is fair game.
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Besides, with the size of his army (as evidenced by the graphs), he should be expanding more / needs to be expanding. And the AI will probably do just that.
But I will switch him to AI this evening like I said I was going to.