Texas was the flash point of tensions between the U.S. and Mexico as the result of repeated attacks by the Mexican bandit Poncho Villa into U.S. territory. The Mexican government seemed reluctant or incapable of dealing with this problem. President Woodrow Wilson called troops of the National Guard of the States into Federal service. While serving on the Mexican Border they were state troops in the service of the U.S., and the State had the authority to appoint and promote officers, and furnish recruits for the units as needed. The States and the Guard will never understand why the period during which it was on the Mexican Border was not utilized to organize the Army, including the National Guard, into divisions at least, and armies and corps, if possible, and comparable to those in effect in the European armies of the time. Common sense would seem to have dictated such a procedure, for the war in Europe had been raging for more than two years, and it was becoming more apparent that we would be involved sooner or later.
In May 1916, five thousand Guardsmen from Arizona, Texas and New Mexico were activated and by July 110,000 Guardsmen were on the border. The National Guard could not be used on foreign soil only to guard the border. This allowed General Pershing to invade with regular forces. The experience of soldiering in such large numbers gave the Guard very important experience that will be of help in World War I. The National Defense Act of 1916 gave the Federal government permission to send the Guard outside the U.S.