In the opening days of the Iraq invasion in 2003, then secretary of defense Donald Rumsfeld infamously quipped, “You go to war with the army you have, not the army you might want or wish to have at a later time.” The offhand remark ignited indignation, but the United States had the Army it wanted. This Army won in the opening days of the Iraq War and excelled in the preferred American way of war—high-intensity combat underpinned by cutting-edge technology.
But this style of warfare is infrequent and brief. Despite the US military’s institutional preference on preparing for conventional conflict, irregular warfare (IW) remains the most prevalent form of warfare since 1945. This trend shows no signs of change in the twenty-first century. The United States cannot opt out of these messy wars, and must be ready for irregular warfare in the conflicts of the future.