I gave played that map once and won it. I would expand as normal early game, the key difference between this map and other maps is that only 1 can win it. So alliances are never going to last. Use this to your advantage, if two players attack you, remind them that only one can win it. This may cause them both to send in less troops as they don't want to have they "ally" losing less troops than them. Diplomacy in this map is important. In a more personal note, I never betray an ally, but as only one player in this map can win, "backstabbing" isn't really a thing in my opinion so "ally" up players and then attack them when it suites you. I did not have to do this strategy but it could work nonetheless.
If a larger power emerges, try to get other players to join you in fighting them.
Its hard to say exactly how to win it as each game is different but perhaps you gained something from this