On June 3, 1916, United States President Woodrow Wilson signs into law the National Defense Act, which expanded the size and scope of the National Guard—the network of states’ militias that had been developing steadily since colonial times—and guaranteed its status as the nation’s permanent reserve force.

Though Theodore Roosevelt and other Republicans were pushing for U.S. intervention in World War I, Wilson, elected in 1912, maintained a position of neutrality throughout the first several years of the war. In the first half of 1916, however, with forces from the regular U.S. Army as well as the National Guard called out to face Mexican rebel leader Pancho Villa during his raids on states in the American Southwest, Wilson and Congress saw the need to reinforce the nation’s armed forces and increase U.S. military preparedness. The National Defense Act, ratified by Congress in May 1916 and signed by Wilson on June 3, brought the states’ militias more under federal control and gave the president authority, in case of war or national emergency, to mobilize the National Guard for the duration of the emergency.

The National Defense Act mandated that the term National Guard be used to refer to the combined network of states’ militias that became the primary reserve force for the U.S. Army. The term had first been adopted by New York’s militia in the years before the Civil War in honor of the Marquis de Lafayette, a French hero of the American Revolution who commanded the Garde Nationale during the early days of the French Revolution in 1789. The National Defense Act also set qualifications for National Guard officers, allowing them to attend Army schools; all National Guard units would now be organized according to the standards of regular Army units. For the first time, National Guardsmen would receive payment from the federal government not only for their annual training—which was increased from 5 to 15 days—but also for their drills, which were also increased, from 24 per year to 48. Finally, the National Defense Act formally established the Reserve Officer Training Corps (ROTC) to train and prepare high school and college students for Army service.

Also in June 1916, Wilson secured passage of the Naval Appropriations Act, which set out to create a U.S. Navy equal to the most powerful in the world—Britain’s—by 1925. That November, Wilson was re-elected with the campaign slogan, "He kept us out of the war." His success was due less to his neutrality, however, than to his record on domestic policy, as U.S. public opinion—as well as the president’s own—had begun to move closer in line with those who favored intervention. By the following spring, Wilson had moved his country to the brink of war after continued German attacks on American interests at sea. On April 2, 1917, he would go before Congress to ask for a declaration of war. Four days later, the U.S. formally entered World War I.