The essential insight from Vietnam is that the crucial elements in war are not smarter tactics, better generals or more malleable popular support but clear-headed thinking about policy and strategy that aligns ways, means and ends relative to national interests, national will and the enemy’s potential. In Vietnam, the United States failed that test. Sadly, it has failed again in Iraq and Afghanistan.

Colonel Gian P. Gentile directs the American History Program at West Point. In 2006, he commanded a combat battalion in West Baghdad. He holds a PhD in history from Stanford University.