Well the way other countries usually get involved in war is they are urged to, are invaded, or have their own political reasons. Or they are allies with one of the nations in a war. So there could be any reason as to why the planet is entering the war. Maybe it isn't even supposed to for a while and he ships out to fight in space, then the war ends up there anyways. It would mean he left way before he "needed" to or was personally involved, Pria and her mom could still have reason to flee, and it wouldn't make him a horrible blood-thirsty sort of character.