The United States in World War I — A Guide to America’s Role in the Great War


The United States of America, led by President Woodrow Wilson, maintained a neutral position during the early years of the “Great War.” However, persistent agitation from Germany finally pulled America into the war in 1917. The American Expeditionary Forces (AEF), led by General John J. Pershing played a key role in helping bring World War I to an end and secure victory for the Allied Powers.

President Woodrow Wilson, Portrait, Cootes

Official Portrait of President Woodrow Wilson by Frank Graham Cootes. Image Source: Wikipedia.

The United States Enters World War I

On April 2, 1917, President Woodrow Wilson appeared before a joint session of Congress where the formally requested a Declaration of War against Germany. Wilson based his request on Germany’s policy of “Unrestricted Submarine Warfare” in the North Atlantic and the Mediterranean, along with Germany’s effort to enter into a military alliance with Mexico against the United States. The Senate responded by approving a resolution to declare war on Germany, on April 4, 1917. The House of Representatives approved the resolution on April 6, officially declaring war on Germany. Later that year, on December 7, 1917, the United States declared war on Germany’s primary ally, Austria-Hungary.

World War 1, Uncle Sam I Want You Recruiting Poster
This iconic poster was created by James Montgomery Flagg for United States Army recruitment during World War I. Image Source: Library of Congress.

American Neutrality and World War I

When the “Great War” started in Europe in 1914, the United States maintained a neutral position. Many Americans wanted to stay out of it, as did President Woodrow Wilson, who opposed the war. In fact, Wilson sent one of his advisors, Edward M. House, to Europe to work on a peace agreement. The effort was unsuccessful, and as the war dragged on, several incidents took place that slowly pulled Wilson and the United States closer to the brink of war.

Germany Unleashes Unrestricted Submarine Warfare

On February 4, 1915, Admiral Hugo von Pohl, commander of the German High Seas Fleet, issued a proclamation that warned all ships sailing through the “waters around Great Britain and Ireland” were at risk of being attacked by the German Navy, primarily submarines. The policy is referred to as “Unrestricted Submarine Warfare,” and it specifically announced the seas around Great Britain and Ireland were a “War Zone” as far as the Germans were concerned.

The Sinking of the Lusitania

Ignoring warnings against travel on Allied ships, the RMS Lusitania, a British cruise liner — a passenger ship — sailed from New York on May 1, 1915, heading for Liverpool. By May 7, the Lusitania was in British waters, off the southern tip of Ireland. A German U-boat — submarine — spotted the Lusitania and fired a torpedo at the ship. The torpedo struck the ship and sank it, killing over 1,100 people, including 128 Americans.

Americans were divided over how to respond. Some wanted to stay out of the war, but others, including former President Theodore Roosevelt, wanted an immediate military response. However, Wilson continued his cautious approach to the war, but he did threaten to end diplomatic relations with Germany. He demanded an apology and financial compensation for the victims. 

Sinking of the Lusitania, 1915, Illustration
This contemporary illustration by Norman Wilkinson depicts the Lusitania sinking. Image Source: Wikipedia.

Wilson also demanded modifications to the submarine warfare policy, which was, in terms of the war, the most important demand. In September, the Germans changed the policy and prohibited attacks on passenger ships. The move eased the tension between the United States and Germany — but it was temporary.

Theodore Roosevelt was appalled at the American response. He wrote to a friend and said, he was “pretty well disgusted with our government and with the way our people acquiesce in and support it.”

Election of 1916

Wilson was reelected for a second term in 1916, running on the slogan, “He Kept Us Out of War.” The Democratic Party also warned that if Americans elected Republican candidate Charles Evans Hughes, the nation would plunge into the war. The election was close, but Wilson won, making him the first Democrat since Andrew Jackson to win a second consecutive term in the White House.

Germany Resumes Unrestricted Submarine Warfare

Seeking to bring about the defeat of Great Britain in 1917, Kaiser Wilhelm II of Germany suggested restoring the full policy of Unrestricted Submarine Warfare. Although there were concerns it would violate the agreement with the United States, the Germans proceeded. German leaders were certain the United States would respond with military force but hoped to defeat the Allied Powers and end the war before it could mobilize.

On January 31, Count Johann von Bernstorff, the German Ambassador to the United States, informed U.S. Secretary of State Robert Lansing that Germany would restart Unrestricted Submarine Warfare on February 1. President Wilson responded by cutting diplomatic ties with Germany on February 3. However, he still refused to ask Congress for a Declaration of War.

Over the next two months, German submarines targeted and sank American ships, causing the deaths of American seamen and citizens. Despite opposition from Congress, Wilson issued an Executive Order, instructing the U.S. Navy to support American merchant ships with Navy personnel, and equipment.

The Zimmerman Telegram

In late February, another issue with Germany came to light when British intelligence notified the United States it had intercepted and decoded a secret transmission sent by Germany to Mexico. In the transmission — known as the Zimmerman Telegram — Germany proposed an alliance between the two nations — violating the Monroe Doctrine.

Germany wanted Mexico to declare war on the United States. In return, Germany offered to help recover the territory it lost to the United States in the aftermath of the Mexican-American War. 

On March 3, Germany confirmed the message was legitimate, enraging Americans, and leaving American neutrality hanging by a thread.

The United States Prepares for World War I

Wilson met with his Cabinet on March 20 and the members agreed it was time to ask Congress for a formal Declaration of War. On April 2, Wilson spoke in front of a joint session of Congress, and within a week, the “Joint Resolution Declaring that a State of War exists between the Imperial German Government and the Government and the people of the United States” was passed. On April 6, 1917, The United States was officially at war.

Wilson and his Secretary of War, Newton D. Baker saw a need to expand both the Regular Army (full-time soldiers), the National Army (volunteers), and the National Guard (local militia). In response, Congress passed the Selective Service Act of 1917, which established local draft boards. Over the course of the war, nearly 3 million Americans would be drafted.

Background and Causes of World War I in Europe

Bosnian Crisis of 1908

On October 5, 1908, Austria-Hungary, one of the most powerful nations in Central Europe, announced it was annexing — taking control — of the territory of Bosnia and Herzegovina. European nations protested the move, especially Serbia. The so-called “Bosnian Crisis” was resolved by the 1909 Treaty of Berlin. Austria-Hungary retained control of Bosnia and Herzegovina, but the crisis increased tension between Austria-Hungary and its neighbors, especially Serbia, Italy, and Russia. The crisis, in fact, set the stage for World War I.

The Assassination of Archduke Franz Ferdinand

Nearly 6 years later, on June 28, 1914, Archduke Franz Ferdinand of Austria-Hungary and his wife, Sophie, Duchess of Hohenberg, were visiting Sarajevo, the capital of Bosnia-Herzegovina. 

A group of Serbian nationalists, still outraged over the annexation of Bosnia and Herzegovina, devised a plan to assassinate the Archduke during the visit. The group was supported by a Serbian military group known as the Black Hand and may have also had help from the Serbian government.

Assassination of Archduke Ferdinand, Illustration
This illustration depicts the assassination of Archduke Ferdinand and his wife. Image Source: Wikipedia.

On the morning of the 28th, the assassins positioned themselves along the Archduke’s motorcade route. At 10:10 a.m., one of the assassins threw a bomb into the Archduke’s car, but it bounced off a seat and into the street, where it exploded.

The motorcade continued, and another assassin, Gavrilo Princip, moved into position to carry out the mission. Princip was near a food shop along the route when the cars took a wrong turn. When they stopped to turn around, Princip rushed the Archduke’s car and fatally shot the Archduke and the Duchess at close range. Princip was seized and arrested right away. Later that morning, the Archduke and Duchess died from their wounds. 

In the immediate aftermath of the assassination, there were anti-Serbian riots in Sarajevo and  Austria-Hungary. The military had to be called in to restore order.

The July Ultimatum

On July 23, Austria-Hungary sent a formal letter to the Serbian government, asking it to respect the Treaty of Berlin and its authority over Bosnia and Herzegovina. The letter, known as the “July Ultimatum,” made specific demands — and gave Serbia 48 hours to comply.

However, the next day, Serbian troops crossed the Danube River into Austria-Hungary. Austro-Hungarian soldiers fired at them, but over their heads, as a warning. Serbia responded to the July Ultimatum and the incident on the border by mobilizing its military.

The Great War Begins

On July 28, Austria-Hungary declared war on Serbia and mobilized a portion of its armed forces. This led Russia and France, under the provisions of a treaty they signed in 1892, to mobilize their armies.

By the end of the year, Europe was engulfed in a war between the Central Powers of Germany, Austria-Hungary, and the Ottoman Empire and the Allies of France, Great Britain, Russia, and Italy. 

By the war’s end in 1918, the “Great War” would consume the world, claim more than 16 million lives, and radically alter how wars are fought. Unfortunately, the resolution of the war also put the pieces in place for World War II.

America’s Role in World War I

Once the United States entered the war, the American Expeditionary Forces (AEF) was established under the command of General John J. Pershing. The AEF was sent to Europe and played a major role in several key battles and campaigns. As of June 1918, over 660,000 members of the AEF had been transported to France. By November, the number was closer to  2 million.

General John J Pershing, Portrait, Horydczak
General John J. Pershing. Image Source: Library of Congress.

Germany’s Spring Offensive

While the AEF assembled in France, the Germans launched “Operation Michael” — a spring offensive on the Western Front. German leaders believed the offensive would allow them to win the war before the AEF reinforced the Allied forces. The Germans advanced to within 75 miles of Paris. It looked like the war was going to be over soon, but the offensive stalled. The Germans tried several offensives against various Allied positions in order to push ahead to Paris — Operation Georgette, Operation Blucher, Operation Yorck, and Operation Marne. 

Americans Join the Fight

On May 29, American troops were involved in combat for the first time. The 1st Division of the AEF fought the Germans at Cantigny.

As more Americans arrived, they were deployed along the Western Front where they fought in many battles, alongside men from Britain, Canada, Australia, and France.

In July, Americans helped push the Germans back at the Second Battle of the Marne, after the German Spring Offensive stalled.

100 Days Offensive

On August 8, 1918, the Allied forces launched a counteroffensive against the Germans. The Battle of Amiens officially started what is known as the “100 Days Offensive.” 

Around that time, the Germans realized the war could not be won with military force, and it would only be a matter of time until more American reinforcements arrived.

Still, the fighting continued. The Battle of Albert took place on August 21. Allied forces attacked the Germans, who were forced to withdraw on September 2. The Germans fell back to the Hindenburg Line, a defensive line they built during the winter of 1916–1917.

Soon after, both Austria-Hungary and Germany tried to make peace with some of the nations, but they were rejected.

The Meuse-Argonne Offensive

In September, the Allies moved into positions along the north and center of the Hindenberg Line. The Germans continued to fight but were pushed back behind the line.

With Pershing in command of Allied Forces, including the AEF, the Meuse-Argonne Offensive was launched on September 26. By late October, the Allies had pushed the Germans out of the Argonne Forest. Continuing their advance, the Allies captured key positions. On November 11, the offensive — and the war — came to an end when the Armistice of Compiegne was signed between Germany and the Allies.

Meuse Argonne Offensive. American Soldiers Firing Machine Gun
Photograph of American soldiers firing a machine gun during the Meuse Argonne Offensive. Image Source: Wikipedia.

United States Naval Support

The United States military was not just involved in the land war. The U.S. Navy patrolled the waters of the Atlantic Ocean, protecting ships, convoys, and shipping lanes. The Navy also played a key role in the sinking of the German submarine U-boats, which had been causing heavy damage to shipping lanes.

The Great War Ends

The Treaty of Versailles was signed in 1919, officially ending the war. Although the treaty marked the end of the “Great War”, it also set the stage for the rise of totalitarian regimes and the eventual outbreak of World War II. Many historians generally agree the harsh terms of the treaty, directed at Germany, along with the subsequent economic and political instability in Europe, were contributing factors to the rise of Hitler and the Nazi Party in Germany.

Significance of the United States in World War I

The participation of the United States in World War I played an important role in shaping the future of the nation. The war effort helped to spur industrialization and economic growth, and also saw a significant number of women and minorities join the workforce. Additionally, the country’s participation in the war, and particularly its role in helping to bring about an end to the conflict, helped to solidify the United States’ position as a world power.

Facts About the United States and World War I

5 Interesting Facts About the United States and World War I

  1. Pershing and the AEF acted independently during the Meuse-Argonne Offensive.
  2. The Meuse-Argonne Offensive is the largest battle in American history.
  3. The Armistice of Compiegne went into effect on November 11, 1917, at precisely 11:11 a.m. — “the eleventh hour of the eleventh day of the eleventh month.”
  4. The terms of the Treaty of Versailles were based in part on Wilson’s “Fourteen Points,” which were designed to create international peace, cooperation, and prosperity.
  5. The United States Senate refused to ratify the Treaty of Versailles.

Important American Military Leaders of World War I

General John J. Pershing — Pershing was the Commander-in-chief of the American Expeditionary Forces (AEF), the main United States military force sent to fight in Europe. He led the AEF throughout the war and was responsible for coordinating the efforts of the American troops with those of their allies.

Colonel George C. Marshall — Marchall served as Pershing’s chief of staff during the war, and played a key role in the organization and logistics of the AEF. He later served as the Chief of Staff of the United States Army during World War II and later as the United States Secretary of State and Secretary of Defense.

General Peyton C. March — March was the chief of staff of the United States Army during the first half of World War I and had a key role in the mobilization of American troops and the development of war plans.

General Tasker H. Bliss — Bliss was a senior military officer and diplomat, and one of the American representatives at the negotiations that ended World War I. He also served as the chief of staff of the United States Army from 1917 to 1918.

General William L. Sibert — Sibert led the 1st Division during the war, the first division of the American Expeditionary Forces to arrive in Europe.

General Hunter Liggett — Liggett led the 1st Corps during the war and played a key role in the Meuse-Argonne Offensive, one of the final and most important battles of the war for the AEF.

General Douglas MacArthur — After the United States declared, MacArthur helped establish the 42nd Division, which was made up of members of the National Guard. He received the Croix de Guerre from French General Georges de Bazelaire. MacArthur commanded troops during the Champagne-Marne Offensive, the Battle of Saint-Mihiel, and the Meuse-Argonne Offensive.

American Heroes of World War I

Several American soldiers from World War I are recognized as heroes for their actions during the war, including:

Sergeant Alvin York — York was a Tennessee farmer who became one of the most decorated — and famous — American soldiers of the war. He received the Congressional Medal of Honor for leading an attack on a German machine gun nest, in which he and his men killed several German soldiers and captured 132 others. York was nicknamed, “Sergeant York.”

Sergeant Henry Johnson — Johnson was an African American soldier who served in the 369th Infantry Regiment. He received the Croix de Guerre, France’s highest military award, for his actions during a night-time raid when he defended himself and a fellow soldier against a group of German soldiers, despite being outnumbered and wounded. Johnson was the first American soldier in World War I to receive the Croix de Guerre. He was posthumously awarded the Medal of Honor by President Barack Obama in 2015.

Sergeant Henry Johnson, WW 1, Croix de Guerre
Sgt. Henry Johnson of the 369th Infantry Regiment was awarded the French Croix de Guerre for bravery. Image Source: U.S. Army.

Lieutenant Colonel Teddy Roosevelt Jr. — Roosevelt was the eldest son of former President Theodore Roosevelt. During World War I, he commanded the 26th Regiment in the 1st Division and fought in the Battle of Cantigny. He received the Distinguished Service Cross for his actions during the war. When he returned to the United States, he helped found an organization that eventually became The American Legion. He returned to service during World War II where he led the 4th Infantry Division in the Battle of Normandy. In fact, he was the only General who landed with the first wave of troops on Omaha Beach. He was awarded the Medal of Honor in 1944.

Corporal Frank Luke Jr. — Luke was an Arizona-born “balloon buster” pilot and the United States Army’s second-highest scoring ace of World War I, known for his aggressive tactics and flying skills. He was the first airman to receive the Medal of Honor. Luke was killed on a mission that took place during the first phase of the Meuse-Argonne Offensive.

Captain Eddie Rickenbacker — Rickenbacker was a fighter pilot who had 26 victories in the war — the most of any American. He received the Medal of Honor. When the armistice was signed on November 11, he flew over the site so he could witness the event.

Lieutenant David S. Ingalls — Ingalls was a pilot and the Navy’s only flying ace of World War I.

Lieutenant Quentin Roosevelt — He was the youngest son of former President Theodore Roosevelt and a pilot during the war. He was killed in action in 1918. He was posthumously awarded the Croix de Guerre with Palm for his bravery.

George S. Patton — During the war, Patton rose to prominence as a tank commander. He commanded the 1st Provisional Tank Brigade and provided support to the U.S. I Corps in the Meuse-Argonne Offensive. Patton was wounded while he led some men and a tank during an attack. He was awarded the Distinguished Service Medal and Purple Heart.

World War 1 APUSH Study Guide

This video from Heimler’s History covers Unit 7 Topic 5 of the AP U.S. History curriculum which is part of Period 7 (1898–1945). Also, be sure to look at our Guide to the AP US History Exam.

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  • Article Title The United States in World War I — A Guide to America’s Role in the Great War
  • Date 1914–1918
  • Author
  • Keywords World War I, The Great War, United States, Woodrow Wilson, American Neutrality, Unrestricted Submarine Warfare, Sinking of the Lusitania, Zimmerman Telegram, Meuse-Argonne Offensive
  • Website Name American History Central
  • Access Date July 15, 2024
  • Publisher R.Squared Communications, LLC
  • Original Published Date
  • Date of Last Update February 1, 2024