Atrocities occur in  wars. This is an observation, not an excuse. And they become more likely the longer a soldier is in combat. War is brutal and it brutalizes the souls of warriors. Some resist the brutalization better than others, but no one can see death that often and not be changed. Just as important, the enemy is dehumanized. You cannot fight and fear him for years and not come to see him as someone alien to you. Even worse, when the enemy and the population are difficult to distinguish, as is the case in a counterinsurgency, the fear and rage extends to everyone. 

There is another secret to American success -- both in controlling the oceans and taking advantage of European failures -- that lies in an often-misunderstood economic structure called Bretton Woods. Even before World War II ended, the United States had leveraged its position as the largest economy and military to convince all of the Western allies -- most of whose governments were in exile at the time -- to sign onto the Bretton Woods accords. The states committed to the formation of the International Monetary Fund and World Bank to assist with the expected post-War reconstruction. Considering the general destitution of Western Europe at the time, this, in essence, was a U.S. commitment to finance if not outright fund that reconstruction. Because of that, the U.S. dollar was the obvious and only choice to serve as the global currency.

But Bretton Woods was about more than currency regimes and international institutions; its deeper purpose lay in two other features that are often overlooked. The United States would open its markets to participating states' exports while not requiring reciprocal access for its own. In exchange, participating states would grant the United States deference in the crafting of security policy. NATO quickly emerged as the organization through which this policy was pursued.

Global history from 1500 to 1945 is a lengthy treatise of increasing contact and conflict among a series of great regional powers. Some of these powers achieved supra-regional empires, with the Spanish, French and English being the most obvious. Several regional powers -- Austria, Germany, Ottoman Turkey and Japan -- also succeeded in extending their writ over huge tracts of territory during parts of this period. And several secondary powers -- the Netherlands, Poland, China and Portugal -- had periods of relative strength. Yet the two world wars massively devastated all of these powers. No battles were fought in the mainland United States. Not a single American factory was ever bombed. Alone among the world's powers in 1945, the United States was not only functional but thriving.