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.