Mexican Revolution: Battle of Ambos Nogales: U.S. Army forces skirmish against Mexican Carrancistas in the only battle of World War I fought on American soil.

The Mexican Revolution was an extended sequence of armed regional conflicts in Mexico from 20 November 1910 to 1 December 1920. It has been called "the defining event of modern Mexican history". It saw the destruction of the Federal Army, its replacement by a revolutionary army, and the transformation of Mexican culture and government. The northern Constitutionalist faction prevailed on the battlefield and drafted the present-day Constitution of Mexico, which aimed to create a strong central government. Revolutionary generals held power from 1920 to 1940. The revolutionary conflict was primarily a civil war, but foreign powers, having important economic and strategic interests in Mexico, figured in the outcome of Mexico's power struggles; the U.S. involvement was particularly high. The conflict led to the deaths of around one million people, mostly non-combatants.

The Battle of Ambos Nogales, or as it is known in Mexico La batalla del 27 de agosto, was an engagement fought on 27 August 1918 between Mexican military and civilian militia forces and elements of U.S. Army troops of the 35th Infantry Regiment, who were reinforced by the Buffalo Soldiers of the 10th Cavalry Regiment, and commanded by Lt. Col. Frederick J. Herman. The American soldiers and militia forces were stationed in Nogales, Arizona, and the Mexican soldiers and armed Mexican militia were in Nogales, Sonora. This battle was notable for being a significant confrontation between U.S. and Mexican forces during the Border War, which took place in the context of the Mexican Revolution and the First World War.

The United States Army (USA) is the primary land service branch of the United States Department of Defense. It is designated as the Army of the United States in the United States Constitution. It operates under the authority, direction, and control of the United States secretary of defense. It is one of the six armed forces and one of the eight uniformed services of the United States. The Army is the most senior branch in order of precedence amongst the armed services. It has its roots in the Continental Army, formed on 14 June 1775 to fight against the British for independence during the American Revolutionary War (1775–1783). After the Revolutionary War, the Congress of the Confederation created the United States Army on 3 June 1784 to replace the disbanded Continental Army.