American victory in the Cold War looks inevitable in hindsight. It didn't seem that way in the Seventies. And, as Iran reminds us, the enduring legacy of the retreat from Vietnam was the emboldening of other enemies. The forces loosed in the Middle East bedevil to this day, in Iran, and in Lebanon, which Syria invaded shortly after the fall of Saigon and after its dictator had sneeringly told Henry Kissinger, "You've betrayed Vietnam. Someday you're going to sell out Taiwan. And we're going to be around when you get tired of Israel." President Assad understood something that too many...