The Ninetieth Division, known as the "Tough 'Ombres," "Texas' Own," or the "Alamo" division, was activated at Camp Travis on August 25, 1917, under command of Maj. Gen. Henry T. Allen. Texas and Oklahoma furnished the original division, although all states were later represented. The monogram T-O insignia was adopted in France. The division left the United States between June 13 and July 6, 1918, set up headquarters at Aignay-le-Duc, France, and saw action in the Villers-en-Haye and Puvenelle sectors of Lorraine and in the St. Mihiel and Meuse-Argonne operations. Total casualties suffered were 310 officers and 9,400 enlisted men. After the armistice in November 1918, the division moved into Germany for occupation duty. It was sent home for demobilization in May 1919.

During World War II the division was reactivated at Camp Barkeley on March 25, 1942. Motorized in September 1942, but again designated as an infantry division in May 1943, the unit embarked for overseas duty from New York on March 23, 1944, and landed in England on April 5. It saw action on D-Day (June 6) in Normandy. Later it participated in campaigns in Normandy, Northern France, the Ardennes, the Rhineland, and Central Europe. Tentative casualty figures compiled late in 1945 reported 2,963 killed, 14,009 wounded, 1,052 missing, and 442 captured. The division was on occupation duty in Germany until November 1945.

The Ninetieth Division was deactivated on December 27, 1945, at Camp Shanks, New York, and reactivated at Dallas on August 4, 1947, as a part of the Organized Reserve Corps. With headquarters at Dodd Field, Fort Sam Houston, San Antonio, the Ninetieth Army Reserve Command is composed of approximately 9,000 reservists who in 1994 served in 110 units in 50 communities in Texas and New Mexico. The Ninetieth ARCOM soldiers, still known as the "Tough 'Ombres" or "Texas' Own," were not mobilized during the Vietnam War. They were used in civil affairs and psychological operations in Grenada and in postinvasion humanitarian-relief efforts in Panama. In 1990–91 the Ninetieth ARCOM played a major role in the Persian Gulf, where twenty-eight units with more than 2,500 soldiers were deployed to provide combat and service support to the Allied coalition. In 1994 the Ninetieth ARCOM was engaged in a comprehensive drug-demand-reduction program designed to help children in Central America and to support humanitarian work in the construction of roads, schools, and water wells in Honduras, Guatemala, and Belize. Also in 1994 the unit planned and hosted a series of ceremonies commemorating the fiftieth anniversary of the Normandy invasion in France, culminating in 1995 in events recognizing the fiftieth anniversary of VE Day.