The Battle of Ambos Nogales 

On the afternoon of Aug. 27, 1918, a Mexican civilian sparked a small gun battle after crossing from the United States back into Mexico at Nogales, without stopping at the U.S. Customs house. Customs Inspector Arthur G. Barber drew his pistol and chased the man, who was suspected of gun smuggling, followed by two enlisted men. A Mexican officer saw Barber coming across and fired at the customs inspector. The shot missed Barber, but struck and killed one of the other two troops. The remaining troop returned fire, killing the Mexican officer.