The Battle of Ambos Nogales (The Battle of Both Nogales), or as it is known in Mexico La batalla del 27 de agosto (The Battle of 27 August), 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.

Prior to the late 1910s, the international border between the two Nogaleses was a wide-open boulevard named International Street, but during the course of the decade the violence associated with the Mexican Revolution and growing hysteria related to World War I brought stricter U.S. control of the border. Anti-foreign sentiment grew in the border region with the publicizing of the German Empire's Zimmermann telegram in February 1917. (Some U.S. military historians of the 10th Cavalry and 25th Infantry later claimed German military advisors encouraged Mexican rebels under General Francisco "Pancho" Villa to fight against the U.S. in Nogales.) Related to the World War I anti-foreign sentiment, the shooting deaths of Mexican nationals at the border by U.S. soldiers in Nogales in early 1918 increased racial tensions in the two border towns. As a result of the 27 August battle, the U.S. and Mexico agreed to divide the two border communities with a chain-link border fence, the first of many permanent incarnations of the U.S.Mexico border wall between the two cities along the two countries' border.

The Mexican Revolution (Spanish: Revolución Mexicana) was an extended sequence of armed regional conflicts in Mexico from 1910 to 1920. It has been called "the defining event of modern Mexican history." It resulted in the destruction of the Federal Army and its replacement with a revolutionary army, transformed 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, with revolutionary generals holding 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 United States played an especially significant role.Although the decades-long regime of President Porfirio Díaz (1876–1911) was increasingly unpopular, there was no foreboding that a revolution was about to break out in 1910. The aging Díaz failed to find a controlled solution to presidential succession, resulting in a power struggle among competing elites and the middle classes, which occurred during a period of intense labor unrest, exemplified by the Cananea and Río Blanco strikes. When wealthy northern landowner Francisco I. Madero challenged Díaz in the 1910 presidential election and Díaz jailed him, Madero called for an armed uprising against Díaz in the Plan of San Luis Potosí. Rebellions broke out in Morelos, but most prominently in northern Mexico. The Federal Army was unable to suppress the widespread uprisings, showing the military's weakness and encouraging the rebels. Díaz resigned in May 1911 and went into exile, an interim government installed until elections could be held, the Federal Army was retained, and revolutionary forces demobilized. The first phase of the Revolution was relatively bloodless and short-lived.

Madero was elected President, taking office in November 1911. He immediately faced the armed rebellion of Emiliano Zapata in Morelos, where peasants demanded rapid action on agrarian reform. Politically inexperienced, Madero's government was fragile, and further regional rebellions broke out. In February 1913, prominent army generals from the Diaz regime staged a coup d'etat in Mexico City, forcing Madero and Vice President Pino Suárez to resign, and few days later both were murdered by orders of new President, Victoriano Huerta. A new and bloody phase of the Revolution ensued when coalition of northerners opposed to the counter-revolutionary regime of Huerta, the Constitutionalist Army. The Constitutionalists were led by Governor of Coahuila, Venustiano Carranza. Zapata's forces continued their armed rebellion in Morelos. Huerta's regime lasted from February 1913 to July 1914, with the Federal Army defeated by revolutionary armies. The revolutionary armies then fought each other, with the Constitutionalist faction under Carranza defeating the army of former ally Pancho Villa by the summer of 1915.

Carranza consolidated power and a new constitution was promulgated in February 1917. The Mexican Constitution of 1917 established universal male suffrage, promoted secularism, workers' rights, economic nationalism and land reform, and enhanced the power of the federal government. Carranza became President of Mexico in 1917, serving a term ending in 1920. He attempted to impose a civilian successor, prompting northern revolutionary generals to rebel. Carranza fled Mexico City and was killed. From 1920 to 1940, revolutionary generals held office, a period when State power became more centralized and revolutionary reforms implemented, bringing the military under control of the civilian government. The Revolution was a decade-long civil war, with a new political leadership that gained power and legitimacy through their participation in revolutionary conflicts. The political party they founded, which would become the Institutional Revolutionary Party, ruled Mexico until the presidential election of 2000, when an opposition party won. Even the conservative winner of that election, Vicente Fox, contended his election was heir to the 1910 democratic election of Francisco Madero, thereby claiming the heritage and legitimacy from the Revolution.