When World War I erupted in Europe in 1914, the United States initially maintained a position of neutrality, following its long-standing tradition of avoiding European conflicts. However, a series of events gradually pulled America into what would become known as the "Great War." The U.S. entry in 1917 helped tip the balance toward Allied victory and thrust America onto the world stage as a major power.
Causes of World War I: MANIA
The assassination in June 1914 was like lighting a match in a room full of gasoline. Countries quickly took sides based on their alliance systems. What started as a local conflict spread across Europe and eventually around the world as nations honored their promises to support each other.
The root causes of World War I can be remembered using the acronym MANIA:
- Militarism: European powers were engaged in an arms race, building up their military forces
- Alliances: Complex defense agreements meant any local conflict could escalate quickly
- Nationalism: Intense pride in one's nation led to competition and hostility
- Imperialism: European powers competed for colonial possessions and resources
- Assassination: The killing of Archduke Franz Ferdinand of Austria-Hungary by a Serbian nationalist sparked the war
The conflict quickly divided Europe into two main alliances:
| Central Powers | Allied Powers |
|---|---|
| Germany | Great Britain |
| Austria-Hungary | France |
| Ottoman Empire | Russia (until 1917) |
| Bulgaria | Italy (after 1915) |
| United States (after 1917) |
America's Initial Neutrality (1914-1917)
America tried to stay out of the European war by declaring neutrality. Wilson urged Americans to be "impartial in thought as well as action." This policy made sense given America's distance from Europe and its tradition of avoiding foreign entanglements dating back to George Washington.
However, maintaining true neutrality proved difficult for several reasons:
- Economic ties: American trade with Britain and France was significantly larger than with Germany
- Financial interests: U.S. banks loaned the Allies about 2.5 billion dollars compared to only 56 million dollars to the Central Powers
- Public sentiment: German actions, as portrayed in American media, gradually turned public opinion against Germany
- British propaganda: British control of transatlantic cables allowed them to shape American perceptions of the war
Path to American Involvement
Germany's actions eventually made it impossible for America to remain neutral. The sinking of passenger ships, unrestricted submarine warfare, and the Zimmermann Telegram pushed public opinion toward war. Wilson's patience finally ran out in April 1917 when he asked Congress for a declaration of war.
Three major factors eventually pushed the United States toward war:
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The Lusitania Incident (1915): Germany's submarine warfare policy led to the torpedoing of the British passenger liner Lusitania, killing 128 Americans. Though the ship was secretly carrying munitions, the incident outraged Americans. Germany temporarily agreed to limit submarine attacks after U.S. diplomatic pressure.
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Resumption of Unrestricted Submarine Warfare (1917): In February 1917, Germany announced it would resume unrestricted submarine warfare, attacking any ships in the war zone, including those from neutral countries. This decision was a calculated risk that Britain could be defeated before America could effectively enter the war.
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The Zimmermann Telegram (1917): British intelligence intercepted and decoded a message from German Foreign Minister Arthur Zimmermann to Mexico, proposing an alliance against the United States. Germany offered to help Mexico reclaim territories lost in the Mexican-American War if the U.S. entered the conflict. When published, this telegram inflamed American public opinion.
Military Preparedness and Mobilization
America had to build a fighting force very quickly. The small peacetime army was not ready for a major war. The draft brought in millions of new soldiers, while factories switched from making consumer goods to producing weapons, ammunition, and supplies for the military.
When the United States entered the war, its military was woefully unprepared for a major conflict. The country quickly transformed itself for war:
- The Selective Service Act (May 1917) required all men aged 21-30 (later expanded to 18-45) to register for the draft
- Nearly 24 million men registered, and 2.8 million were drafted
- The regular army grew from about 128,000 to over 4 million by war's end
- Industry rapidly converted to war production
American Expeditionary Force (AEF)
General John J. "Black Jack" Pershing insisted on keeping American forces together rather than using them as replacements for Allied units. He wanted U.S. troops to fight as an independent army with their own identity and leadership, which helped establish America as a major military power.
General John J. Pershing commanded the American Expeditionary Force (AEF) in Europe. He insisted that American troops:
- Operate as an independent force rather than as replacements in British and French units
- Use aggressive, open-field tactics rather than the defensive trench warfare that had led to stalemate
- Maintain a distinct American identity while cooperating with Allied forces
The first American troops arrived in France in June 1917, but large-scale American involvement didn't begin until spring 1918. Key American military contributions included:
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Château-Thierry and Belleau Wood (June 1918): American forces helped stop a German offensive that threatened Paris, boosting Allied morale and demonstrating American fighting capability.
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Second Battle of the Marne (July 1918): American troops helped halt Germany's final major offensive and began pushing German forces back.
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St. Mihiel Offensive (September 1918): The first operation planned and executed under complete American command successfully reduced a German salient (bulge) that had existed for four years.
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Meuse-Argonne Offensive (September-November 1918): The largest American operation of the war involved 1.2 million American troops in a 47-day campaign that helped break German resistance. This brutal campaign cost 26,000 American lives.
The Fourteen Points and Peace Efforts
Wilson's Fourteen Points offered a new approach to peace. Instead of punishing the losers, Wilson wanted to fix the problems that caused the war. His plan included fair treatment for all nations and a League of Nations to prevent future conflicts through cooperation and negotiation.
As the war neared its end, Wilson outlined his vision for a just and lasting peace. In January 1918, he presented his Fourteen Points to Congress, which included:
- Open peace treaties instead of secret diplomacy
- Freedom of the seas
- Removal of economic barriers to trade
- Reduction of armaments
- Self-determination for nationalities (allowing ethnic groups to form their own nations)
- Creation of a League of Nations to preserve peace
Germany, facing imminent defeat, agreed to an armistice based on Wilson's Fourteen Points. The fighting ended on November 11, 1918, at 11:00 a.m. – the eleventh hour of the eleventh day of the eleventh month.
The Paris Peace Conference and Treaty of Versailles
Wilson faced tough opposition at the peace conference. Britain and France had suffered greatly during the war and wanted revenge. They forced Wilson to compromise on many of his ideals in order to create the League of Nations, which he saw as the key to lasting peace.
The resulting Treaty of Versailles included terms that can be remembered using the acronym BRAT:
- Blame: Germany was forced to accept sole responsibility for causing the war
- Reparations: Germany had to pay enormous financial penalties (about $33 billion)
- Armaments: German military forces were severely limited
- Territory: Germany lost its colonies and about 13% of its European territory
Wilson did secure the creation of the League of Nations, but had to compromise on many of his other points.
Senate Rejection of the Treaty
The treaty battle revealed a deep divide in American politics. Many Republicans feared that the League of Nations would drag America into future wars. Senator Lodge demanded changes to protect American independence, but Wilson refused to compromise and insisted on an all-or-nothing approach.
The Treaty of Versailles faced stiff opposition in the U.S. Senate, where a two-thirds majority was required for ratification. Opposition came from several sources:
- "Irreconcilables" opposed any involvement in European affairs
- "Reservationists," led by Senator Henry Cabot Lodge, supported the treaty with amendments to protect American sovereignty
- Concerns about Article X of the League of Nations covenant, which could potentially require the U.S. to take military action without congressional approval
Wilson refused to accept any compromises, insisting on an all-or-nothing approach. He suffered a severe stroke in October 1919 that left him partially paralyzed. Without effective leadership, the treaty failed to gain the necessary votes in the Senate. The United States never ratified the Treaty of Versailles and never joined the League of Nations.
War's Impact on America's Global Role
World War I changed America's place in the world, even as the country tried to avoid new commitments. The U.S. emerged as an economic powerhouse with a proven military capability. However, Americans remained divided about their global role, leading to a retreat into isolation during the 1920s despite the country's new power and influence.
Though the United States rejected the Treaty of Versailles, the war fundamentally changed America's position in the world. The conflict transformed the nation from a debtor country to the world's leading creditor, with European nations owing America over $10 billion.
Vocabulary
The following words are mentioned explicitly in the College Board Course and Exam Description for this topic.
| Term | Definition |
|---|---|
| Allies | The coalition of nations including Britain, France, and Russia that fought against the Central Powers in World War I, which the U.S. supported through its entry into the war. |
| American Expeditionary Forces | The U.S. military forces sent to Europe during World War I, whose entry helped shift the balance of the conflict in favor of the Allies. |
| democratic principles | Values based on democratic governance and self-determination that Wilson argued the U.S. should defend by entering World War I. |
| humanitarian principles | Values centered on human welfare and the protection of human rights, which Woodrow Wilson cited as justification for U.S. entry into World War I. |
| League of Nations | An international organization proposed after World War I to maintain peace, which the U.S. Senate refused to allow the United States to join. |
| neutrality | The policy of not taking sides in a conflict or war, which the United States initially maintained at the beginning of World War I. |
| noninvolvement | A U.S. foreign policy tradition of avoiding military and political entanglement in European affairs. |
| Treaty of Versailles | The peace treaty ending World War I that the U.S. Senate refused to ratify, despite Wilson's involvement in its negotiation. |
Frequently Asked Questions
Why did the US stay neutral at first in World War I?
At first the United States stayed neutral for several linked reasons. Longstanding isolationist tradition kept Americans wary of European wars; many wanted to avoid entangling alliances. Ethnic and political divisions at home (large German and Irish immigrant populations, plus pro-British sentiment) made unified support for one side difficult. Economically the U.S. traded with both sides and profited more by staying neutral. President Woodrow Wilson also framed neutrality as moral leadership—“impartial in thought as well as in action”—while hoping to broker peace. Early in the war the government protested violations of neutral rights (notably German unrestricted submarine warfare and the Lusitania sinking) but held off declaring war until events like renewed unrestricted submarines and the Zimmermann Telegram pushed Wilson to act in 1917. For AP review, connect this to KC-7.3.II and Wilsonian idealism; see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and grab practice questions at (https://library.fiveable.me/practice/ap-us-history).
What made America finally join World War I?
Short answer: the U.S. stayed neutral at first, but Germany’s return to unrestricted submarine warfare (sinking merchant ships, including the Lusitania in 1915) that threatened American lives and commerce, plus the Zimmermann Telegram (Germany’s offer to Mexico of U.S. territory if it joined the war), pushed public opinion and Wilson to act. Wilson framed entry as defending democracy and humanitarian principles, asking Congress for a declaration in April 1917. The Selective Service Act and creation of the American Expeditionary Forces under John J. Pershing followed, while the Committee on Public Information mobilized support at home. U.S. manpower and resources helped tip the balance for the Allies, though the Senate later refused to ratify the Treaty of Versailles or join the League of Nations. For AP review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
Can someone explain Wilson's Fourteen Points in simple terms?
Wilson’s Fourteen Points were his 1918 blueprint for a fair, lasting peace after World War I. In simple terms: they called for open diplomacy (no secret treaties), free seas and trade, arms reductions, self-determination for national groups (new borders based on ethnicity), fair treatment of colonies, and a new international body to settle disputes—the League of Nations. Points 1–10 focused on specific territorial and policy fixes; 11–13 addressed boundary changes in Europe and the Ottoman Empire; Point 14 proposed the League. Wilsonian idealism shaped U.S. entry into the war and his push at Versailles, but the Senate refused to ratify the Treaty of Versailles or join the League (Senate ratification debate), which limited the Fourteen Points’ impact. For AP study, link this to U.S. involvement, postwar diplomacy, and the Treaty of Versailles (see Fiveable’s Topic 7.5 study guide: https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt). Practice questions: https://library.fiveable.me/practice/ap-us-history.
How big of a role did American soldiers actually play in WWI combat?
Short answer: American soldiers played a crucial but limited combat role. The American Expeditionary Forces (AEF), led by John J. Pershing, sent about 2 million U.S. troops to Europe (roughly 4.7 million were mobilized overall). Only a portion saw front-line combat, but U.S. manpower and fresh units in 1918—especially during the Meuse-Argonne Offensive—helped relieve exhausted Allied armies and tip the strategic balance toward an Allied victory. The CED’s wording is exact: U.S. combat power was relatively limited in scope but decisive in timing and logistics. For AP essays and short answers, link this to Wilson’s decision to enter the war, total-war mobilization at home (Selective Service, War Industries Board), and the October–November 1918 offensives. For a quick Topic 7.5 review, see the Fiveable study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice more with Fiveable’s APUSH problems (https://library.fiveable.me/practice/ap-us-history).
What's the difference between the Treaty of Versailles and the League of Nations?
Treaty of Versailles = the actual peace agreement that ended World War I in 1919; it set territorial changes, reparations, and punishments for Germany and included the Covenant (charter) creating the League of Nations. It reflected compromises among Allied leaders and only partly followed Wilson’s Fourteen Points. The League of Nations = an international organization created to provide collective security and a forum for diplomacy to prevent future wars. Conceptually it expressed Wilsonian idealism; practically it was a standing body (with assemblies, council, and dispute-resolution mechanisms) rather than a single treaty text. Why it matters for APUSH: Wilson led U.S. diplomacy at Versailles, but the U.S. Senate refused to ratify the Treaty of Versailles and so the U.S. didn’t join the League (Senate ratification debate is a required CED point). For review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
Why did the Senate refuse to ratify the Treaty of Versailles?
The Senate refused to ratify the Treaty of Versailles mainly because of opposition to the League of Nations and concerns about Article X tying the U.S. to future foreign commitments. Republicans led by Senator Henry Cabot Lodge (the “reservationists”) wanted amendments/ reservations to protect Congress’s war-declaring power; the “irreconcilables” rejected the treaty entirely. Wilson’s unwillingness to accept compromise and his national tour left treaty supporters divided. Because ratification required a two-thirds Senate vote and Wilson refused Lodge’s changes, the treaty failed—so the U.S. signed separate peace treaties and didn’t join the League. This debate is a key example of postwar isolationism vs. Wilsonian idealism (CED keywords: Woodrow Wilson, Treaty of Versailles, League of Nations, Senate ratification debate). For a focused review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
I'm confused about why Wilson wanted to join the League of Nations but Congress said no
Wilson wanted the U.S. to join the League of Nations because of his Fourteen Points and “Wilsonian idealism”: he thought a global organization could prevent future wars and protect democracy (key CED items: Fourteen Points, Treaty of Versailles, League of Nations). After leading peace talks, Wilson pushed the Treaty of Versailles with League membership included. Congress (the Senate) rejected ratification mainly for constitutional and partisan reasons. Treaty ratification requires a two-thirds Senate vote (Article II), and Senators led by Henry Cabot Lodge worried the League’s Article X collective-security obligations would limit Congress’s constitutional power to declare war. Reservationists wanted amendments; irreconcilables opposed membership entirely. Wilson’s refusal to compromise helped the treaty fail. The Senate ratification debate is a specific CED learning target (Topic 7.5). For a quick review, check the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
What were the main consequences of the US entering World War I?
When the U.S. entered WWI in 1917 the biggest consequences were diplomatic, military, and domestic. - Military/diplomatic: American Expeditionary Forces under John J. Pershing helped tip the balance toward the Allies (Meuse-Argonne Offensive; Armistice 1918), and Wilson pushed his Fourteen Points at Versailles—but the Senate refused to ratify the Treaty of Versailles or join the League of Nations (CED: KC-7.3.II). - Total war mobilization: Selective Service, War Industries Board, Liberty Bonds, and economic coordination expanded federal power and industrial production. - Home front/politics: Committee on Public Information mobilized public opinion; Espionage and Sedition Acts restricted civil liberties; wartime mobilization accelerated the Great Migration and women’s workforce roles, strengthening the push for suffrage. - Aftermath: heavy casualties, veterans’ needs, a brief postwar isolationism and the 1919–1920 Red Scare shaped 1920s policy. For more AP-aligned review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
How do I write a DBQ essay about American neutrality in WWI?
Start with a clear thesis that answers the prompt: e.g., “Although the U.S. declared neutrality in 1914 to preserve trade and avoid European entanglements, a mix of economic ties to the Allies, German unrestricted submarine warfare (including Lusitania), and the Zimmermann Telegram pushed the U.S. to enter the war.” In your intro also contextualize briefly (Wilsonian idealism, Progressive-era internationalism, 1898 legacy). During the 15-minute reading period, group documents into categories (political/diplomatic, economic, military/propaganda, public opinion). Use at least four documents to support your line of reasoning and cite one piece of outside evidence (Selective Service Act, AEF/Pershing, or Committee on Public Information). For two docs explain POV/purpose (e.g., government memo vs. newspaper). End by acknowledging complexity (continuity of noninvolvement vs. break with tradition—Treaty of Versailles/League of Nations rejection). Follow DBQ rules: thesis, contextualize, use ≥4 docs, include outside evidence, source two docs, and aim for complexity. For topic review, see the Fiveable study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
Did the American Expeditionary Forces actually help the Allies win the war?
Short answer: Yes—the American Expeditionary Forces (AEF) didn’t win World War I alone, but U.S. entry in 1917 decisively tipped the balance for the Allies. Under John J. Pershing, about 2 million U.S. soldiers served in Europe (roughly 1.3 million overseas by late 1918). American factories and shipping also supplied fresh matériel and credit. Militarily the AEF played a limited role at first, but in 1918 U.S. troops were key in stopping German offensives and in the Meuse-Argonne Offensive, which helped exhaust German manpower and morale. Politically and diplomatically, U.S. entry strengthened Allied resolve and hastened the Armistice. For AP exam purposes, tie this to KC-7.3.II (limited combat role but tipping the balance) and use specifics (Pershing, Selective Service, Meuse-Argonne) in short-answer/LEQ/DBQ responses. Review Topic 7.5 study guide for details (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice questions (https://library.fiveable.me/practice/ap-us-history).
What does "departing from noninvolvement in European affairs" mean exactly?
It means the U.S. broke with its long-standing policy of staying out of European wars and power politics. Instead of staying neutral or focused on the Western Hemisphere, Woodrow Wilson pushed the country to join World War I in 1917 to defend “humanitarian and democratic principles” (CED KC-7.3.II). Practically, that shift was driven by events like unrestricted submarine warfare, the sinking of the Lusitania, and the Zimmermann Telegram, and it led to mobilization (Selective Service, War Industries Board, AEF under Pershing), Wilson’s Fourteen Points, and active involvement in the Paris negotiations—even though the Senate later refused the Treaty of Versailles and League membership. For the AP exam, expect DBQ/LEQ prompts asking you to explain causes and consequences of this departure; use the Topic 7.5 study guide for targeted review (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and try practice questions (https://library.fiveable.me/practice/ap-us-history).
Why was Wilson so involved in postwar negotiations if America didn't want to join international organizations?
Wilson pushed to lead the peace because he believed shaping the settlement would prevent another war and protect U.S. interests—not because every American wanted membership in a global club. His Fourteen Points and demand for a League of Nations reflected “Wilsonian idealism”: moral leadership, self-determination, and a rules-based order that he thought would secure long-term peace (CED keywords: Fourteen Points, Treaty of Versailles, League of Nations). Politically, Wilson wanted the U.S. to have a decisive voice at Versailles so terms wouldn’t punish allies or leave power vacuums that hurt American trade and security. But domestic politics mattered: many senators (led by Lodge) feared Article X and loss of congressional war powers, so isolationist sentiment and constitutional concerns led the Senate to refuse ratification. For AP review, link Wilson’s diplomatic goals to causes/consequences of U.S. involvement and the ratification debate (see the Topic 7.5 study guide: https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt). For practice, check Fiveable’s AP problems (https://library.fiveable.me/practice/ap-us-history).
What were Wilson's humanitarian and democratic principles that he talked about?
Wilson’s “humanitarian and democratic principles” were the ideas he used to justify leaving neutrality and entering WWI: defend democracy, self-determination for nations, and protect civilians from unjust warfare. His Fourteen Points (free seas, open diplomacy/no secret treaties, reduced armaments, free trade, and national self-determination) and the goal to “make the world safe for democracy” summed this up. He framed U.S. entry as moral: stop unrestricted submarine warfare and defend neutral rights, then shape a postwar order via a League of Nations to prevent future aggression. On the AP exam, connect this rhetoric to causes of U.S. involvement (CED KC-7.3.II), Wilsonian idealism, the Fourteen Points, and the Senate’s later refusal to ratify the Treaty of Versailles. For a focused review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and more practice questions (https://library.fiveable.me/practice/ap-us-history).
How did US entry into WWI change American foreign policy forever?
US entry in 1917 marked a turning point: the U.S. abandoned long-standing noninvolvement in European affairs and acted as an international power defending “humanitarian and democratic principles” (CED). Militarily the American Expeditionary Forces helped tip the balance in 1918; diplomatically Wilson pushed the Fourteen Points and led at Versailles—but the Senate refused to ratify the Treaty of Versailles or join the League of Nations. The result was lasting change: the U.S. gained global influence and practice in large-scale mobilization (Selective Service, War Industries Board, CPI, Espionage/Sedition Acts), and a new “Wilsonian” vocabulary for promoting democracy abroad. At the same time, domestic politics produced a temporary retreat to isolationism—showing continuity and change you should analyze on LEQs or DBQs. For a focused review, see the Topic 7.5 study guide (https://library.fiveable.me/ap-us-history/unit-7/world-war-i-military-diplomacy/study-guide/4wZDa2Pak8FfrKeucUqt) and practice problems (https://library.fiveable.me/practice/ap-us-history).