The core defense debate of our time is how to make the US military more effective at irregular warfare (IW) and stability, security, transition, and reconstruction (SSTR) operations in weak or failing states while still retaining some aspect of its strategic capabilities for major power warfare. Given the current global security system and likely future American strategy, the configuration that provides the best balance is one with ground forces about the size of today's, with the Marines and the Army organized around a geographic division of labor, but with enough cross-training that each service could, in an emergency, operate outside its normal region. While the ground forces must retain the capability for large-scale conventional combat, they clearly should focus most of their efforts on the requirements of IW/SSTR. This may not be the force we would prefer to have in 2020, but it is the most realistic one for the coming decade.