This paper uses a system of differential equations to describe the insurgency in Iraq. The system has four possible outcomes or cases: (1) The U.S.-led coalition increases in size and the number of attacks by the insurgents increases. (2) The size of the U.S.-led coalition decreases and the number of attacks by insurgents decreases. (3) The size of the U.S.-led coalition increases and the number of insurgent attacks decreases. (4) The size of the U.S.-led coalition decreases and the number of insurgent attacks increases. Which case is relevant depends on the recruitment rates of the U.S.-led coalition and insurgents as well as the combat effectiveness of both sides. Policy implications are provided.