The U.S. Army between 1900 and the outbreak of World War I

World War I recruiting poster

The changes that occurred within the U.S. Army between the turn of the century and the eve of the first world war presaged America’s emergence as a world power. America during these times was increasingly dependent upon its military for the conduct of military-type tasks beyond the continental United States. A significant driver of this increased dependency was increased international (mostly economic) competition. It was felt, particularly by the Roosevelt Administration that this increase in competition between the nations of Europe actually increased the likelihood of war. Hence, the corresponding need for greater U.S. military preparedness.

The Army advanced in terms of professionalism and preparedness in spite of the nation’s long tradition of hostility to these things. Despite its success in the Spanish-American war, it also made great strides in terms of capabilities.

Guiding all its other changes, the Army reorganized as an institution. A war college was established in 1900 which Secretary of War Elihu Root used to form the nucleus of a general staff—the brain of the Army. This led to the passage of the General Staff Act in 1903 and the creation of the position of chief of staff. Under the law, 45 staff officers supported the chief of staff. Some served in Washington “while others served in the headquarters of the Army’s geographic departments, which supervised field forces.” In this one may see, in embryonic form, the rise of today’s geographic combatant commands.


Complementing the Army’s top-level reorganization was a corresponding growth of tactical force. Working against this steady increase in manpower and military professionalism, however, was the nation’s predisposition against a large standing army. The solution, it seemed, was to establish a reserve force, under federal control, that could operate beyond the nation’s borders. To accomplish this, Congress tinkered with reforming the National Guard. In 1903, the Dick Act was passed which essentially established two militias—the Organized Militia, or the National Guard, and the unorganized mass of male citizens, ages 18-45, creating within this group menu of mandatory service obligations both to the state and federal level. A second Militia Act of 1908 (the Dick Act being considered the first) removed time and geographic constraints for Guard service. To this was added the establishment of a National Guard Bureau whose head reported to the Secretary of War, not the general staff. A Quartermaster Department was established in 1912 which added a corps of 6000 logistical specialists. Authorized U.S. Army strength in 1900 stood at 101,713, supported by expenditures of $134 million. By 1920 that force had doubled to 204,292 on the strength of $1.6 billion in spending. In between, the Army (and Navy) had mobilized and demobilized an expeditionary force of more than 4.5 million men, a force “truly beyond the imagination of policy makers in the nineteenth century.

Institutional reorganization and a growth in its manpower were not the complete story of the Army’s changes during the first two decades of the 20th Century. Rapid changes in technology drove improvements in small arms capabilities, artillery, machine guns, and communications. Most noticeably, the Army began to gravitate away from the horse towards mechanization as the capabilities of the combustion engine harnessed to a wheeled chassis were realized. Trucks and automobiles appeared in many types of units, cutting transportation time and costs. Moreover, the airplane added a new dimension to the battlefield. As aircraft technology developed, the Army began to grow an aviation field and expand its capabilities for conducting intelligence, surveillance, and reconnaissance operations.

Together, these changes, which represented a gradual shift in national military strategy, drove changes in military doctrine, especially the idea that national defense was limited to threats faced in the near Pacific or within the Western Hemisphere. World War I would validate the need for every one of these changes, plus more.