The nation helps because it defines the borders and they are clear.
Do you know the number 1 reason for most wars and killings and destruction in Europe over the centuries (even before religion)
? It's those f*ucking borders!
Jailed into borders is not the natural state for the Europeans, wandering and roaming freely is!(Even today the war in the ME is about those f*ucking borders)
. Maybe you in the US can't compare how it is having your natural environment being split up, taken away, claimed by some "border".
However, it hampers cooperation, when you think your nation is best and all others are inferior to you.
There are many, many nations who fight each other...there are only a few tribes (Celts, Slavs, Germanics) in Europe and only one race (White)...
Where do you think the danger of going to war against each other proofed more true?
When was the last nation war?
When was the last tribal war?
When was the last race war?
...says all, doesn't it!