If you let one player get too powerful you will get attacked. Unfortunetly to survive you'll need to make lots of unofficial alliances and back-stabbing (not doing what you said you would or worse attacking your supposed ally) will label you as a traitor not just for this game but for future games with those opponents as well.
So it all gets a bit tense. Usually the first one to crack will lose the game and hand it to the player who didn't do anything. You want to be the player who somehow always looks strong enough not to attack and has pieces spare with which to make an attack against a player who is clearly not long for the game.
Its a harsh world, but that's the fun - how can you negotiate the impossible. I often seem to just by making it awkward to attack me, and I've learnt from another great strategy player that its best not to stand out but follow the crowd.
Can you survive?