> Countries and most borders are just an abstraction.

Not true. Patriotism is very real. It's an affection for a group of people and for the ideals of those people. To some lesser extent it's also love for the geography of your land. But patriotism is rarer in the west than it once was. Also, if a country's territory is invaded by an enemy, at least some of its people will go to fight to protect their families from the oncoming enemies.