High self-esteem.

To be honest, yes... I can't imagine what I would do if I were a pacifist. Would I form federations around myself? Well, maybe that's also a normal way to win, but I'm not sure...

No, this is a lousy way to win, although it does work in general – you attack an enemy empire, but you demand that they don't transfer planets to you, but liberate them, you win, the liberated planets create a state that is absolutely loyal to you, you make them your vassals, and then you integrate them into your empire. American-style democracy.
However, I didn't do that anyway, because it's tedious and doesn't fit the role-playing. If we are democrats and xenophiles, then we shouldn't start wars without a reason, and there is no reason, so we can close the game and play for an eternal and happy peace.
Interesting lessons in cyber-strategy from Ple-Sen, it's good that I played in single-player mode and also didn't bother to destroy everyone with torpedoes.