Climate change will often affect countries that lack the capacity to deal with its impacts. The internal stresses will be dangerous for those countries, and the demands on outside parties that step in to assist will be great. The Department of Defense will inevitably be a major player, and it must center its effort on preparing its allies and partners to get ready for, and cope with, environmental changes and their consequences. The wars the Nation is fighting make many loath to dedicate resources to climate change, yet until the adjustment is made, disasters will continue to occur and security crises will be the spinoff. Attention to this looming source of trouble now will make Washington more prepared for response, redirect the U.S. military toward the most likely scenarios, enhance the international security environment, and strengthen the Nation’s global standing.