Not all
The tbs games Alpha Centauri and Civilization III allow one to strive for a peaceful path and use diplomacy but I admit that war is inevidible.
The game Galactic Civilizations is the closest I have seen to an adult none violent game. You can play as a pacificist and rely heavily on diplomacy. You are even given moral choices to make along the way and you are graded accordingly. War is still hard to avoid at the higher difficulty levels but it becomes secondary to the game.
Unfortunately, these are exceptions that prove the rule rather than proving you wrong.