After August 1914 there was no public consensus in the United States about the war in Europe. Families long settled in the United States had a sense of international isolation. Recent immigrants had ties to European affairs but their different origins and sympathies gave voice to varied opinions. Small numbers of Americans volunteered for foreign military service. Some sent aide to combatants or relief agencies. The United States government practiced neutrality and encouraged the citizenry to do so.
American churches prayed for peace and neutrality. American governmental and private missions attempted peace negotiations. Business interests and public sentiment began to favor the Allies over the Central Powers. Ties to France and England were strong and British media was more accessible to Americans. Exporters to Germany complained of trade lost to the successful Allied blockade. Protests shrank when the Allies’ purchases replaced lost German orders many times over.
Neutral Americans could not ignore regular compelling news from Europe. The drama and tragedy of conflict and the power and novel technology of modern warfare drew a broad audience. Domestic conflict in Mexico also captured popular attention. German submarines sank Allied ships without warning like the liner Lusitania in 1915. Civilians, including Americans, were injured or killed angering the American public and government. In a world at war Americans were moved to military preparation, antipathy toward Germany, and sympathy with the Allies. Germany hesitated and agreed to spare passenger ships and warn merchantmen prior to attacking.
Legislation in early 1916 authorized further naval expansion of an already large and modern United States Navy. The United States Army and National Guard together totaled just over 200,000 men in 1915. In 1916 the War Department authorized expansion to total 575,000 for both, and organization of reserves. The National Guard became liable for foreign deployment. A National Research Council was established to investigate military technology. Private organizations supported by former President Teddy Roosevelt opened civilian martial training programs. Relatively small numbers of American citizens continued to volunteer with belligerent forces, often as non-combatants. President Wilson was reelected in November 1916 with the slogan “he kept us out of war” but it was armed neutrality.
In February 1917 the German Navy resumed unrestricted submarine warfare. Ships were again indiscriminately attacked without warning. Their growing submarine fleet made a blockade of England possible, and if the United States declared war submarines would decisively delay their forces arrival in Europe. American indignation swelled and Britain released a decoded German message, the Zimmerman telegram. It offered a German alliance with Mexico if the United States joined the Allies. Debate between Americans for neutrality and those for war came to a head. President Wilson argued for a war against autocratic governments “to make the world safe for democracy.” After four days of congressional debate the United States declared war on April 6, 1917.
Many Americans had anticipated the conflict. Declaring war started government and military mobilization in earnest. In May conscription was approved and General Pershing named to lead the American Expeditionary Force (AEF). In June Pershing arrived in France followed shortly by the first American troops. This began the buildup of American combat, administration, supply, and support troops that eventually numbered several million. On July 4, 1917 the 16th United States Infantry Regiment paraded in Paris. On July 14, Bastille Day, Louis Ganella of the Medical Corps, became the first American soldier wounded by the enemy. He was serving with the British near Arras, France.
During the remainder of 1917 American combat troops were trained by Allied combat veterans and contingents sent to the front beside experienced Allied troops. The service troops, Engineers, Transportation, and Medical Corps, among others, worked from the frontlines to the ports of arrival supporting the Allies and the growth of American forces. The United States Navy sent aviation and anti-submarine forces to the French coast to protect arriving troop and supply ships. French and British commanders requested that large American units be put under their command. General Pershing insisted on building an independent American Army though some regiments were detached to serve with the British and French Armies.
In the first months of 1918 events occurred with repercussions beyond the end of the war. President Wilson announced his “Fourteen Points”, territorial changes and international agreements intended to assure lasting peace. In March Russia declared a separate peace with Germany, freeing many German troops to fight on the Western Front. In late March an influenza pandemic was began in the United States. Millions of soldiers and refugees on the move spread influenza worldwide killing tens of millions.
The Imperial German Army transferred forces to the Western Front. Employing elite assault troops and moving massed artillery from place to place they mounted multiple offensives from early April into July, intending to bring the Allies to the bargaining table before American troops could enter battle en masse. In the crisis more United States Army units were placed under Allied command. They performed well in combat at Cantigny, Chateau Thierry, and Belleau Wood. German forces failed to break the Allies on the Western Front. The United States Navy joined Allies laying the North Sea Mine Barrage. American skill and industrial ability made it possible to complete the barrier faster with fewer mines, reducing the German submarine threat.
American Forces also fought outside the Western Front in France and Belgium. In July the 332nd United States Infantry Regiment deployed to Northern Italy to fight Austro-Hungarian forces. Over a hundred Red Cross ambulance drivers had been in Italy since December 1917, and Army and Navy aircrew flew on the Italian Front. Further east from September 1918 to August 1919 the 339thUnited States Infantry Regiment with attached Engineers and Medical staff served with Naval Landing parties and British troops against Russian Bolsheviks at Arkangel and Kola, Russia. Larger American contingents landed in August 1918 with Allied forces at Vladivostok to guard that port and part of the Trans-Siberian Railway. They stayed until April 1920.
In July 1918 the Allies began a series of their own offensives. The French and British attacked on the Somme in early August being joined by additional British forces later in the month. Americans joined with the French in the Aisne-Marne Offensive in July. The United States First Army was established in August. It engaged in the St. Mihiel offensive and then the Meuse-Argonne offensive with French Forces. Some detached American Regiments continued to operate with French Belgian and British forces. The 2nd United States Army was established in October. The Allied forces continued the offensives into the fall. By early November Americans closed up to and crossed the River Meuse. They had cut vital train lines behind the German front and reached the gates of Sedan.
On November 11, 1918 fighting ended after the Germans accepted the Allied conditions for an Armistice. The Kaiser had abdicated two days before. German forces fell back out of Belgium and France, including the provinces of Alsace and Lorraine. Allies forces advanced to the Rhine and crossed it to establish bridgeheads on German territory. President Wilson arrived in Paris in December and on January 4, 1919 the Peace Conference was convened. A peace treaty was signed on June 28 and ratified by Germany on July 9, 1919.