Will 2014 bring another Great War? My bet is almost certainly not, but with a note of caution. Claims that war is "inconceivable" are not statements about what is possible in the world, but rather, about what our limited minds can conceive. The fact that Presidents Obama and Xi understand that war would be folly for both China and the US is relevant but not dispositive. None of the leaders in Europe of 1914 would have chosen the war they got and that in the end they all lost. By 1918, the Kaiser was gone, the Austro-Hungarian Empire dissolved, the Tsar overthrown by the Bolsheviks, France bled for a generation, and England shorn of the flower of its youth and treasure. Given a chance for a do-over, none of the leaders would have made the choices he did.

Thus as we look forward with hope to the year ahead, reflection on mistakes made a century ago reminds us of the perils of complacency.

Graham Allison is Director of the Harvard Kennedy School’s Belfer Center for Science and International Affairs.

Image: U.S. Air Force/Flickr.

Editor's Note: The following article has been updated since publication.