"Should be?" What a strange choice of words. Surely you aren't proposing that war is the only kind of interaction that competing nations "should be" permitted to have? America and Japan have been economic rivals for decades, despite being political allies. Many Europeans see America as a rival, finding our geopolitical and cultural dominance to be troubling, but they're still our allies rather than our enemies. Contrary to the Cold War fantasies of American red-baiters, the Soviet and Chinese Communist Parties couldn't stand each other, disagreed with each other's interpretations of Marxism, and competed with one another for leadership of the communist movement, and yet they never went to war with one another. There are many forms of rivalry other than warfare. Conflict or competition can be waged through economics, diplomacy, political maneuvering, cultural influence, scientific and technological innovation, etc.