Game already ended after my 690BC turn with him giving up. I landed a lone exploring warrior on his isle and he did me the favour of killing it. I signed up the Sumerians (on his isle) against him and he signed Cleo against me later. Which gave me a good chance to take gems from her - triggering my GA.
After upgrading my warriors I landed 8 legions on a hill near one of his coastal cities. I razed that and 3 turns later I took another, leaving him without horses and any sizable force to strike back. I must admit that the rng favored me, but I have 4 galleys of reinforcements in the pic below that would have landed next turn.
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