We know that often holding those who have carried out mass atrocities accountable is at times our best tool to prevent future atrocities.

When it came to the Vietnam War, Mr. McNamara was an early advocate of escalation but came to realize the flaws in the American approach earlier than many of his colleagues. Yet in public, he continued to defend the war.

I believe the United States is the greatest country on Earth. I really do.

Re-examining our reasoning is not something that has come naturally to American statesmen.

From Richard Holbrooke - and I miss him every day - I learned two things. One, prioritization: Never take your eye off the longer-term reforms. The other thing is, he was a hell of a schmoozer! So I should take advantage of my Irish love of beer and gift of the gab, and build relationships. That's a cherished part of the job, asking someone, "How did you get to be the Rwandan ambassador?" I try to take advantage of the fact that I hope to be here at least until the president's term ends getting to know my colleagues.

As even a democracy like the United States has shown, waging war can benefit a leader in several ways: it can rally citizens around the flag, it can distract them from bleak economic times, and it can enrich a country's elites.

We need to find means for cooperation.