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On March 26, 1913, Venustiano Carranza issued the Plan de Guadalupe, which refused to recognize Huerta as president and called for war between the two factions. Soon after the assassination of President Madero, Carranza returned to Mexico to fight Huerta, but with only a handful of comrades. However, by 1913 his forces had swelled into an army of thousands, called the División del Norte (Northern Division). Villa and his army, along with Emiliano Zapata and Álvaro Obregón, united with Carranza to fight against Huerta. In March 1914 Carranza traveled to Ciudad Juárez, which served as rebellion's capital for the remainder of the struggle with Huerta. In April 1914 U.S. opposition to Huerta had reached its peak, blockading the regime's ability to resupply from abroad. Carranza trying to keep his nationalistic credentials threatened war with the United States. In his spontaneous response to U.S. President Woodrow Wilson Carranza asked "that the president withdraw American troops from Mexico.”

Carranza threatened war with what country in order to maintain credibility nationally?
United States