U.S. General John J. Pershing attacked by Mexican troops

On June 21, 1916, Mexican troops attacked the United States expeditionary force under General Pershing. From the article:

"The controversial U.S. military expedition against Mexican revolutionary Pancho Villa brings the United States and Mexico closer to war when Mexican government troops attack U.S. Brigadier General John J. Pershing’s force at Carrizal, Mexico. The Americans suffered 22 casualties, and more than 30 Mexicans were killed. Against the protests of Venustiano Carranza’s government, Pershing had been penetrating deep into Mexico in pursuit of Pancho Villa. After routing the small Mexican force at Carrizal, the U.S. expedition continued on its southern course.

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."