The coup of February 1913, involving the overthrow and killing of Madero, had decisive effects. ‘Counter-revolution and Constitutionalism’ outlines how Huerta, the interim president, relied on the old Federal Army to support his leadership. In reaction, many of the components of the fragmented Maderista coalition began to reassemble and reorganize. The big northern frontier states—Coahuila, Chihuahua, and Sonora—played a key role under the leadership of Carranza, Obregón, and Villa, alongside the continued Zapatista revolt in Morelos. The rebels made the transition from guerrilla to conventional warfare, aided by the US lifting its arms embargo in early 1914. In August 1914, rebel forces approached Mexico City and Huerta resigned.