In the second half of the 20th century, when America’s leaders heard “preventive war,” they thought about Nazi Germany and Imperial Japan. And for good reason. Both regimes had used the doctrine to justify their attacks in World War II. In August 1939, on the eve of his invasion of Poland, Hitler told his generals that, “we are faced with the hard alternative of either striking or the certainty of being destroyed sooner or later.” In a 2006 journal article, University of Pittsburgh law professor Jules Lobel quoted the Commander of the Japanese fleet, Admiral Yamamoto, as writing that, “[i]n the event of outbreak of war with the United States, there would be little prospect of our operations succeeding unless, at the very outset, we can deal a crushing blow to the main force of the American fleet in Hawaiian waters.”