The Tampico Affair began as a minor incident involving United States Navy sailors and the Mexican Federal Army loyal to Mexican dictator General Victoriano Huerta. On April 9, 1914, nine sailors had come ashore to secure supplies and were detained by Mexican forces. Commanding Admiral Henry Mayo demanded that the US sailors be released, Mexico issue an apology, and raise and salute the US flag along with a 21 gun salute. Mexico refused the demand. US President Woodrow Wilson backed the admiral's demand. Mexicans of all factions of the Mexican Revolution united against the US demands. The conflict escalated when the Americans took the port city of Veracruz, occupying it for more than six months. This contributed to the fall of Huerta, who resigned in July 1914. Since the US did not have diplomatic relations with Mexico following Huerta's seizure of power in 1913, the ABC Powers offered to mediate the conflict, in the Niagara Falls peace conference, held in Canada. The American occupation of Veracruz resulted in widespread anti-American sentiment.

José Victoriano Huerta Márquez was a general in the Mexican Federal Army and 39th President of Mexico, who came to power by coup against the democratically elected government of Francisco I. Madero with the aid of other Mexican generals and the U.S. Ambassador to Mexico. His violent seizure of power set off a new wave of armed conflict in the Mexican Revolution.