Revolutionary General Pancho Villa, who had at one time been supported by the United States, felt betrayed when the Americans backed Carranza. In January 1916, Villa's followers, known as Villistas, attacked a train and killed 16 American businessmen who were aboard. Two months later Villa's men crossed the border into the United States and attacked the town of Columbus, New Mexico, killing an additional 19 Americans. Following these attacks, General Pershing took his forces into Mexico to pursue Pancho Villa. Preceding these events, Middleton's 7th Regiment was sent to Camp Harry J. Jones near Douglas, Arizona to perform border security. While there, Middleton and a squad of his men were fired upon by the Villistas who unsuccessfully attacked the Mexican village of Agua Prieta, across the border from Douglas. While several of Middleton's men were hit, no one was killed, and they all returned with the 7th Regiment back to Fort Bliss in late December 1915. Preparation for war The hunt for Pancho Villa ended unsuccessfully for the Americans. War was raging in Europe, and following several months in Mexico, Pershing was called back to Fort Bliss to begin preparing his troops for this much larger conflict. In April 1917, President Wilson requested that Congress declare war, which they did. The same month Middleton was assigned to Gettysburg National Park where the 7th Regiment would continue its training. Here, he was promoted to first lieutenant on 1 July 1916, after a little more than three and a half years as a second lieutenant. With the pending war, his promotions would become much more frequent, and in less than a year he was promoted to captain, on 15 May 1917, over a month after the American entry into World War I. World War I In preparation for its buildup in strength, the army had to train a large cadre of officers. On 10 June 1917 Middleton was assigned to Fort Myer, Virginia, just outside Washington, D.C. as the adjutant of a reserve officer training camp. These camps were organized to take civilians and turn them into officers in ninety days, and as adjutant Middleton was responsible for directing the flow of paperwork for 2,700 officer candidates. By November 1917, his camp graduated its last class of officers, and Middleton requested to join a combat division. His request was granted and on 21 December 1917 he reported to the 4th Division at