In response, the United States Army, under the direction of General John J. Pershing, launched a punitive expedition into northern Mexico, to find and capture Villa.
In 1914, the United States occupied Veracruz, aiming to cut off supplies of ammunition from the German Empire to Mexico at the start of World War I.
In exchange, the German Empire wanted Mexico's formal support in anticipation of a hypothetical United States entry into the war in Europe.
Violence was at its highest from 1915 to 1919, in response to the Plan de San Diego by Mexican and Tejano insurgents to conquer Texas.
Tensions were further escalated by the Tampico Affair of 9 April 1914, where nine American sailors landed in a restricted dock area and were subsequently detained for an hour and a half.
Francisco I. Madero challenged Porfirio Díaz in the election, who has been a longtime Mexican president but recently sent the citizens into economic struggles.