Michael O’Hanlon offers an analysis of the future of the world’s ground forces: Where are large-scale conflicts or other catastrophes most plausible? Which of these could be important enough to require the option of a military response? And which of these could in turn demand significant numbers of ground forces in their resolution? O’Hanlon is not predicting or advocating big US roles in such operations—only cautioning against overconfidence that we can and will avoid them.