With World War I entering its third year, a controversial U.S. military expedition against Mexican revolutionary Pancho Villa brings the neutral United States closer to war itself, when Mexican government troops attack U.S. Brigadier General John J. Pershing's force at Carrizal, Mexico, on June 21, 1916.
In 1914, following the resignation of Mexican leader Victoriano Huerta, Pancho Villa and his former revolutionary ally Venustiano Carranza battled each other in a struggle for succession. By the end of 1915, Villa had been driven north into the mountains, and the U.S. government recognized General Carranza as the president of Mexico.
In January 1916, to protest President Woodrow Wilson's support for Carranza, Villa executed 16 U.S. citizens at Santa Isabel in northern Mexico. Then, on March 9, he ordered a raid on the border town of Columbus, New Mexico, in which 17 Americans were killed and the center of town was burned. Cavalry from the nearby U.S. Army outpost Camp Furlong pursued the Mexicans, killing several dozen rebels on U.S. soil and in Mexico before turning back. On March 16, under orders from President Wilson, U.S. Brigadier General John J. Pershing launched a punitive expedition into Mexico to capture or kill Villa and disperse his rebels. The expedition eventually involved some 10,000 U.S. troops and personnel. It was the first U.S. military operation to employ mechanized vehicles, including automobiles and airplanes.
For 11 months, Pershing failed to capture the elusive revolutionary, who was aided by his intimate knowledge of the terrain of northern Mexico and his popular support from the people there. Meanwhile, resentment over the U.S. intrusion into Mexican territory led to a diplomatic crisis with Carranza's government in Mexico City. On June 21, 1916, the crisis escalated into violence when Mexican government troops attacked a detachment of the U.S. 10th Cavalry at Carrizal. The Americans suffered 22 casualties, and more than 30 Mexicans were killed.
The U.S. Army's actions in Mexico led Germany's foreign minister, Arthur Zimmermann, to think Mexico might welcome further opportunities to take up arms against its powerful neighbor. In January 1917, Zimmermann sent a telegram to the German ambassador to Mexico proposing a Mexican-German alliance in the case of war between the United States and Germany and promising Mexico financial support and territory–including Texas, New Mexico and Arizona–in return for its support.
In late January 1917, with President Wilson under pressure from the Mexican government and more concerned with the war overseas than with bringing Villa to justice, the Americans were ordered home. The Zimmermann Telegram, intercepted and decoded by British intelligence, reached the U.S. government in February; Wilson authorized the State Department to publish it in early March. Americans were outraged, and public sentiment began to turn irrevocably against Germany. The U.S. formally entered World War I on the side of the Allies on April 6, 1917.
Pancho Villa continued his guerrilla activities in northern Mexico until Adolfo de la Huerta took over the government and drafted a reformist constitution. Villa entered into an amicable agreement with Huerta and agreed to retire from politics. In 1920, the government pardoned Villa; three years later, he was assassinated at his ranch in Parral by an unknown assailant.