## Learning Outcomes

- Explain why the United States declared neutrality in **1914** and why that position became harder to maintain
- Identify the long-term and immediate causes of U.S. entry into World War I in **1917**
- Distinguish between the roles of the **Lusitania**, the **Sussex Pledge**, renewed **unrestricted submarine warfare**, and the **Zimmermann Telegram**
- Analyse how economic ties to the Allies affected U.S. policy
- Explain how Woodrow Wilson justified war in his **April 2, 1917** war message
- Use this topic in causation, DBQ, SAQ, and LEQ responses for AP U.S. History

## AP United States History Syllabus

For the AP United States History, you are expected to understand U.S. entry into World War I, with a focus on the following syllabus points:

- Know that Woodrow Wilson declared U.S. neutrality when war began in Europe in **August 1914**
- Identify how the **British blockade** and U.S. trade and loans tied America more closely to the Allies than to the Central Powers
- Explain how **German U-boat warfare** challenged U.S. claims to neutral rights and freedom of the seas
- Understand why the sinking of the **Lusitania** in **1915** increased anti-German feeling but did not immediately bring the U.S. into war
- Know the importance of the **Arabic Pledge**, **Sussex incident**, and **Sussex Pledge** in delaying war
- Explain why Germany’s resumption of **unrestricted submarine warfare** in **1917** was a direct trigger for intervention
- Identify the significance of the **Zimmermann Telegram** and why it made Germany seem like a direct threat to U.S. security
- Understand Wilson’s argument in his war message that the world must be made **“safe for democracy”**

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. Why did the United States try to remain neutral when World War I began in **1914**?
2. Why did the **Lusitania** matter, and why is it wrong to say it directly caused U.S. entry into the war?
3. What was the **Zimmermann Telegram**, and why did it shift American opinion?
4. How did economic ties to Britain and France make neutrality harder to maintain?
5. What were the two most immediate causes of the U.S. declaration of war in **April 1917**?

## Introduction

The U.S. entry into World War I is one of the clearest APUSH examples of a shift from traditional distance from European wars to much deeper global involvement. The exam often tests this topic through causation: what pushed the United States from neutrality in **1914** to intervention in **1917**?

The strongest answers do not reduce the story to one event. The United States did not enter the war simply because the **Lusitania** sank, and it did not enter only because of idealistic language about democracy. A high-scoring answer shows how long-term pressures, especially trade and diplomacy, combined with immediate triggers in **1917**.

> **Key Term: neutrality**
> A policy of remaining out of a war and treating all belligerents impartially.

### Why neutrality appealed in 1914

When war broke out in Europe in **August 1914**, Woodrow Wilson declared American neutrality. That decision fit older U.S. habits in foreign policy. Many Americans still believed the country should avoid deep involvement in European conflicts. Washington’s Farewell Address and later traditions of staying clear of European power struggles still shaped public opinion.

Neutrality also made political sense at home. The United States had a very mixed population, including immigrants and descendants of immigrants from many of the countries now at war. If Wilson openly backed one side too early, he risked dividing the nation. He hoped instead that the United States could remain above the conflict and perhaps later mediate peace.

> **Key Term: neutral rights**
> The rights claimed by nations not at war, especially the right to trade and travel without unlawful interference by belligerents.

But neutrality in theory was easier than neutrality in practice. The biggest problem was geography and trade. Britain’s navy dominated the Atlantic. That meant Britain could block goods from reaching Germany far more effectively than Germany could interfere with British commerce. Even if the U.S. government declared itself neutral, the actual flow of trade would not be balanced.

American exports and loans increasingly went to Britain and France, not to Germany. This was partly because the British blockade made trade with Germany extremely difficult. That economic pattern mattered because it tied U.S. prosperity more closely to an Allied victory or at least Allied survival. Students often miss the distinction here: trade with the Allies did not itself equal a declaration of war, but it made strict neutrality much harder to sustain.

> **Test Tip:** In an SAQ or LEQ, separate **background causes** from **immediate triggers**. Economic ties and the British blockade are strong background causes. They are not the same as the final triggers in 1917.

Some Americans argued that this meant the U.S. was never truly neutral. That is a defensible interpretation, and it can work well in a DBQ. Still, the best balanced answer explains that Wilson sincerely tried to avoid war at first, even though economic and diplomatic realities pulled the country closer to the Allies.

### How submarine warfare made neutrality unstable

Germany’s main answer to the British blockade was submarine warfare. Because German surface ships could not defeat the British navy, Germany turned to **U-boats**. This raised a legal and moral issue. Under accepted international rules, civilian and merchant ships were supposed to be warned before being attacked. Submarines could not do that effectively without losing the advantage of surprise.

> **Key Term: unrestricted submarine warfare**
> German policy of sinking ships in designated waters without warning, including merchant ships, in violation of U.S. claims to neutral rights.

This is where neutrality began to crack. Wilson believed strongly in freedom of the seas and in the protection of neutral shipping. German submarine attacks threatened both. The most famous early crisis came with the sinking of the **Lusitania** on **May 7, 1915**.

The **Lusitania** was a British passenger liner. Its sinking killed **1,198** people, including **128 Americans**. This caused outrage in the United States and sharply increased anti-German feeling. Yet students must be precise: the U.S. did **not** enter the war in 1915. That mistake loses credit because it collapses a two-year process into one event.

Why, then, does the **Lusitania** matter so much? Because it shifted opinion and made neutrality more fragile. It suggested that American lives were not safe at sea and that German methods violated accepted standards of warfare. At the same time, the ship was also carrying war materials, which gave Germany a justification it used in its defense. That complexity is useful in argument writing: Germany saw the ship as part of the Allied war effort; many Americans saw the attack as barbaric regardless.

Germany temporarily backed down after the backlash. The **Arabic** incident in **1915** brought another promise to limit attacks on passenger ships. Then the **Sussex** crisis in **1916** led to another retreat.

> **Key Term: Sussex Pledge**
> A **1916** German promise to restrict submarine attacks and avoid sinking passenger and merchant ships without warning.

The importance of the **Sussex Pledge** is that it delayed war. It shows Wilson was still trying to preserve peace even after repeated crises. If the U.S. had wanted war at the first excuse, it could have entered earlier. Instead, diplomacy continued.

At the same time, the U.S. began to prepare. The **preparedness movement** pushed for stronger armed forces in case war came.

> **Key Term: preparedness movement**
> A campaign urging the United States to strengthen its military before entering World War I.

Preparedness mattered because it shows opinion was changing before **1917**. The country was not fully pro-war, but more Americans were starting to think neutrality might not hold. Wilson’s **1916** campaign slogan, **“He kept us out of war,”** only worked because many voters still wanted peace. Yet even in that election year, preparedness showed growing anxiety.

> **Test Tip:** If asked about the **Lusitania**, say it was a **turning point in opinion**, not the final cause of war. A precise phrase like that can earn analysis credit.

### Why 1917 changed everything

The final break came in **1917**, when two developments made continued neutrality much less realistic.

First, Germany announced on **January 31, 1917** that it would resume unrestricted submarine warfare beginning **February 1**. This mattered more than the earlier submarine crises because Germany was now openly abandoning the restraints it had previously promised in the **Sussex Pledge**. In effect, Germany signaled that it would attack shipping despite American objections.

This was the strongest immediate cause of war. It threatened U.S. ships, U.S. trade, and U.S. neutral rights all at once. It also told Wilson that diplomacy had failed. If Germany would not respect neutral shipping, then neutrality could not protect American interests.

Second, the **Zimmermann Telegram** pushed public opinion further.

> **Key Term: Zimmermann Telegram**
> A secret German message sent in **January 1917** proposing that Mexico ally with Germany against the United States.

The telegram proposed that if the United States entered the war against Germany, Mexico should attack the U.S. In return, Germany would help Mexico recover **Texas, New Mexico, and Arizona**. Britain intercepted the message, and when it became public in **March 1917**, many Americans were furious.

Why was the telegram so effective? Not because it had a realistic chance of immediate success, but because it made Germany look like a direct threat to U.S. national security. Earlier disputes had centered on ships and trade. Now the issue seemed to involve American territory and the Western Hemisphere itself.

Students often ask which mattered more: unrestricted submarine warfare or the Zimmermann Telegram. The best answer is that unrestricted submarine warfare was probably the more important direct cause, because it made U.S. neutrality impossible at sea. The Zimmermann Telegram then strengthened support for intervention by making the danger seem immediate and local as well as overseas.

A sophisticated answer can also mention the **Russian Revolution** in **March 1917**. When the tsar fell, some Americans found it easier to support the Allied side because Russia no longer looked like such an obvious autocracy. That helped Wilson frame the war more convincingly as a struggle involving democracy, though it was not one of the main direct triggers.

### Wilson’s war message and how to analyse causation

On **April 2, 1917**, Wilson asked Congress for a declaration of war. Congress declared war on Germany on **April 6, 1917**. In his war message, Wilson combined practical and idealistic arguments. He condemned Germany’s submarine campaign as a violation of neutral rights and international law, but he also gave the famous broader claim that **“the world must be made safe for democracy.”**

This is an important APUSH distinction. Wilson’s rhetoric was moral and universal. His policy was also shaped by concrete pressures: shipping losses, diplomacy, security fears, and economic ties to the Allies. Strong essays connect these two levels rather than choosing one and ignoring the other.

Students also need to distinguish three stages clearly:

- **Neutrality**: staying out of the war while claiming impartial rights
- **Armed neutrality**: the idea of defending U.S. shipping while not yet fully entering the war
- **Intervention**: formal declaration of war against Germany

That sequence shows how policy shifted step by step. The move was not sudden in **1915** and not inevitable in **1914**. It developed through repeated crises until the German decisions of **1917** made a break likely.

For APUSH causation, it helps to rank causes:

1. **Immediate direct cause:** renewed unrestricted submarine warfare in **1917**
2. **Second immediate cause:** the **Zimmermann Telegram**
3. **Background causes:** trade and loans to the Allies, British blockade, preparedness, growing anti-German opinion after earlier sinkings
4. **Justifying context:** Wilson’s idealism and democracy language, helped by changes such as the Russian Revolution

If you structure an essay this way, you show more than description. You show judgment.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- Woodrow Wilson declared U.S. neutrality when World War I began in **August 1914**
- Neutrality appealed because many Americans wanted to avoid European wars and the U.S. population was ethnically divided
- The **British blockade** pushed the United States economically closer to the Allies
- U.S. trade and loans increasingly favored Britain and France over Germany
- German **U-boat warfare** challenged U.S. neutral rights and freedom of the seas
- The sinking of the **Lusitania** in **1915** increased anti-German feeling but did not directly bring the U.S. into war
- The **Sussex Pledge** temporarily reduced tensions by promising limits on submarine attacks
- The **preparedness movement** showed that many Americans were beginning to accept possible intervention
- Germany resumed **unrestricted submarine warfare** in **1917**, creating the main immediate cause of U.S. entry
- The **Zimmermann Telegram** made Germany appear to threaten U.S. territory directly
- Wilson asked Congress for war on **April 2, 1917**, and the U.S. declared war on Germany on **April 6, 1917**
- Wilson justified war as both a defense of neutral rights and a fight to make the world safe for democracy

## Key Terms and Concepts

- neutrality
- neutral rights
- unrestricted submarine warfare
- Sussex Pledge
- preparedness movement
- Zimmermann Telegram


World War I: Military and Diplomacy - U.S. enters World War I