The answer is ruefully poignant: Vietnam. McNamara was a stoic believer in the war in Vietnam and initially supported the pouring of soldiers and dollars into the war. "I think it is a very important war," McNamara wrote in April 1964, "and I am pleased to be identified with it and do whatever I can to win it." American involvement in South-East Asia (no doubt a western knee-jerk Cold War response) was greeted with criticism and was opposed by the American populace at the time. This led to McNamara’s labeling as the ‘architect’ of the Vietnam War, in effect also labeling him as the sole reason of the deaths and losses endured by the U.S.A. The war itself came to be known as ‘McNamara’s war’, which he came to regret. He was reported to have said, "I didn't have the answers. All I knew was we were in a hell of a mess”, showing his post-revisionist view on the conflict. When the fog of war lifted, McNamara was able to see the damage ‘his’ war caused, the money wasted on the ‘unwinnable’ war, and the devastation caused by his ‘belief’ that America had the right to intervention in South-East Asian…