Armies in the millions were the norm at the turn of the 20th century. European armies were larger than they had been even before the outbreak of World War I. Millions served on both sides and with them were the most technologically sophisticated and advanced military machinery of the day. Thousands of patents on weaponry were granted in the decade leading up to the war itself. More than 13 million men served in the German Army alone and were widely regarded as the most disciplined army in the world. The British Navy was outfitted with dreadnoughts, the most advanced battleships of the day, and Germany launched the first U-boats, soon to be the terror of Atlantic shipping lanes. When war was declared in 1914, these military mega-powers utilized the maximum potential of their manpower.
Across the Atlantic Ocean though, the U.S. military fell significantly short of their European counterparts. Voices in the United States were echoing the need to prepare the nation’s army and navy for the eventual declaration of war. However, the size and power of the United States’ armed forces paled in comparison, and prominent individuals recognized these detriments. They voiced their concern that the United States was woefully unprepared to fight any war overseas because it lacked the training and resources for large scale combat. A grassroots movement soon developed called the Preparedness Movement where people such as General Leonard Wood, Elihu Root, Henry Stimson, and former President Theodore Roosevelt argued for increased military spending, setting up officer schools, and establish training camps (which eventually formed into the Citizens Military Training Camp in Plattsburg, NY). The Preparedness Movement gained significant traction in 1916 as people advocated for military intervention and increased spending. Reports about trench warfare and poison gas alarmed the U.S. military as well since they had no recent experiences or countermeasures to these new weapons.

(President Woodrow Wilson in Preparedness Parade, Washington D.C., June 1916, American Unofficial Collection of World War I Photographs 1917-1918, Records of the War Department General and Special Staff, 1860-1952, National Archives and Records Administration)
Despite the push for a stronger military, isolationist sentiment in the United States still dominated much of Washington politics. President Woodrow Wilson and the Democratic Party were opposed to the Preparedness Movement and concentrated more on achieving some form of compromised peace or non-intervention pact with Europe. Democratic politicians voiced their concerns of intervening abroad, warmongering, and giving too much political power to big business, which would profit from a rapidly expanding military. President Wilson and Congress routinely debated over the issue, presenting numerous compromises to preparedness advocates in increasing the size of the army and building training camps.
During this time, however, Germany’s unrestricted submarine warfare policy was wrecking havoc on American shipping in the Atlantic, galvanizing the Preparedness argument.Events in North America and not Europe would push Congress to pass legislation sought by the Preparedness Movement. Pancho Villa’s raid on Columbus, New Mexico, called for retaliation by the U.S. Army to neutralize him and his forces. This combined with the long running harassment of U.S. shipping by German U-boats, President Wilson finally threw his support to the Preparedness cause.
On June 3, 1916 the National Defense Act was passed to reorganize the National Guard, expanded the army, created officer training corps, and gave the president authority to federalize troops during a national emergency. The Preparedness Movement accomplished its goal and when the United States intervened in April 1917, its military was better equipped to fight the Central Powers. While trench warfare ferocity was unparalleled in previous wars, US soldiers were now prepared to face such terror that awaited on the Western Front.