Victor Davis Hanson (emphasis added):

Throughout history, the trigger points of war have traditionally been such borderlands — the methoria between Argos and Sparta, the Rhine and Danube as the frontiers of Rome, or the Alsace-Lorraine powder keg between France and Germany. These disputes did not always arise, at least at first, as efforts to invade and conquer a neighbor. They were instead mutual expressions of distinct societies that valued clear-cut borders — not just as matters of economic necessity or military security but also as a means of ensuring that one society could go about its unique business without the interference and hectoring of its neighbors.

Read the whole thing, Why borders matter — and a borderless world is a fantasy