Keith B. Bickel challenges a host of military and strategic theories that treat particular bureaucratic structures, large organizations, and elites as the progenitors of doctrine. This timely study of how the military draws lessons from interventions focuses on the overlooked role that mid-level combat officers play in creating military doctrine. Mars Learning closely evaluates Marine civil and military pacification operations in Haiti, the Dominican Republic, and Nicaragua, and illuminates the debates surrounding the development of Marine Corps' small wars doctrine between 1915 and 1940. The result is compelling evidence of how field experience obtained before 1940 played a role in shaping the Marine Corps' Small Wars Manual and elements of doctrine that exist today. How the Marines organized lessons at that time provides important insights into how doctrine is likely to be generated today in response to post-Cold War interventions around the globe.