What I tend to do sometimes is ally with everyone and then get them to attack each other by convincing them "Hey uh X is winning right now, do you want to attack him together? I can't because I've made peace with him, but I'll gift you my share of drillers [from an outpost no-one else can see]. You can take any mines you capture. [X usually ends up taking it back, and both players start losing lots of Np]" . Usually they're pretty happy to do that (because they don't want X to get 1st place) and they don't suspect I'm actually the one controlling the game pretty much. And basically X starts attacking the attacker and not me, and I end up winning (well thats the idea).
I've only played 2 games so far, and I've used that strategy in both games. I think a more substantial version of that would be that I get everyone to attack each other so that all the pairs of players are engaged in war with each other, and in the meantime I'll just buff up my defense.