[Ryzorian]

In basic terms it comes down to "tribalism". MY group of guys is better than yours. You see it in sports, gameing, anywhere people compete. Nationalism is just Tribalism taken to the next level. Hell, even if we managed to set aside all our differences and become one united world, we would simply fight what ever alien race we came into contact with because it would be Humans verse Aliens.

As long as competition exists, tribalism will exist. There's no point removeing competion because that's what drives us to become better, to improvise, adapt, overcome. Kill competion and you kill humanity.