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By 1917, the war had reached a critical turning point. The entry of the United States gave the Allies a massive new source of manpower and resources, while Germany's last desperate gamble — the Spring Offensive of 1918 — nearly succeeded in winning the war before American forces arrived in strength. This lesson covers the reasons for US entry, the events of 1917–1918, and the final campaigns that led to the armistice.
The United States had maintained a policy of neutrality since 1914, following President Woodrow Wilson's declaration that America would be "neutral in fact as well as in name." However, several factors gradually drew the USA into the conflict.
| Factor | Explanation |
|---|---|
| Unrestricted submarine warfare | Germany's resumption of unrestricted U-boat attacks (February 1917) sank American ships and killed American citizens |
| The sinking of the Lusitania (1915) | 128 Americans died when the British liner was torpedoed. This turned American public opinion against Germany |
| The Zimmermann Telegram (January 1917) | A secret German message proposed a military alliance with Mexico, promising to help Mexico recover Texas, New Mexico, and Arizona. British intelligence intercepted and revealed it, outraging American opinion |
| Economic ties | American banks and businesses had lent billions of dollars to the Allies. An Allied defeat would mean financial ruin |
| Democratic ideals | Wilson framed US entry as a fight to "make the world safe for democracy." The Russian Revolution (February 1917) removed the embarrassment of being allied with an autocratic tsar |
Exam Tip: The Zimmermann Telegram is one of the most important immediate causes of US entry. Be able to explain both what it said and why it was so significant in changing American opinion.
| Date | Event |
|---|---|
| 1 February 1917 | Germany resumes unrestricted submarine warfare |
| 24 February 1917 | Zimmermann Telegram published in American newspapers |
| March 1917 | Russian Revolution begins (Tsar Nicholas II abdicates) |
| 6 April 1917 | USA declares war on Germany |
| June 1917 | First American troops (American Expeditionary Force, commanded by General John Pershing) arrive in France |
| November 1917 | Bolshevik Revolution in Russia; Russia begins to withdraw from the war |
| December 1917 | Russia signs an armistice with Germany |
The USA brought enormous resources to the Allied cause, but it took time for these to have an effect.
| Aspect | Detail |
|---|---|
| Manpower | By November 1918, over 2 million American soldiers were in France |
| Morale | The promise of unlimited American reinforcements boosted Allied morale and demoralised Germany |
| Supplies | American industry provided vast quantities of food, weapons, and raw materials |
| Time lag | It took over a year for the USA to mobilise, train, and transport its forces. This created a window of opportunity for Germany |
With Russia out of the war (the Treaty of Brest-Litovsk was signed in March 1918), Germany could transfer nearly 1 million soldiers from the Eastern Front to the Western Front. General Erich Ludendorff planned a massive offensive to break through the Allied lines and win the war before American forces arrived in full strength.
| Aspect | Detail |
|---|---|
| Where | The Somme sector; aimed at splitting the British and French armies |
| Tactics | Stormtroopers (elite, fast-moving assault troops) bypassed strong points and pushed deep into Allied territory. Preceded by a short, intense bombardment using gas and high-explosive shells |
| Initial success | The Germans advanced up to 40 miles in some areas — the biggest advance on the Western Front since 1914 |
| Scale | Along a 50-mile front; the British Fifth Army was nearly destroyed |
| Offensive | Date | Target |
|---|---|---|
| Operation Georgette | April 1918 | British sector in Flanders |
| Operation Blücher | May 1918 | French lines along the Aisne; Germans reached the Marne, 37 miles from Paris |
| Operation Gneisenau | June 1918 | Further attacks on French positions |
| Reason | Explanation |
|---|---|
| Overextended supply lines | The Germans advanced so fast that they outran their supply lines. Troops were exhausted and hungry |
| Allied reinforcements | Fresh American troops helped plug gaps in the Allied line |
| No strategic reserves | Germany had committed its best troops and had no replacements |
| Allied coordination | In April 1918, Ferdinand Foch was appointed Supreme Allied Commander, improving coordination between British, French, and American forces |
| German morale | German troops, poorly supplied and exhausted, began to lose heart. Some units stopped to loot Allied supply dumps rather than continuing to advance |
Exam Tip: The Spring Offensive is a key turning point. Its failure meant that Germany had used its last chance to win the war. From July 1918 onwards, the Allies were on the offensive, and Germany's defeat was only a matter of time.
From August 1918, the Allies launched a series of devastating offensives that drove the German army back.
| Date | Event |
|---|---|
| 8 August 1918 | Battle of Amiens — the "Black Day of the German Army" (Ludendorff). British, French, and Australian troops, supported by 500 tanks, broke through the German line |
| September–November 1918 | Continuous Allied advances along the entire Western Front |
| October 1918 | Germany's allies (Bulgaria, Ottoman Empire, Austria-Hungary) collapsed and sought armistices |
| 29 September 1918 | Ludendorff tells the Kaiser that the war is lost |
Question (Paper 1, Q7, 12 marks, AO1+AO2): Has the entry of the USA into the war in 1917 been the most important reason for Allied victory? Explain your answer.
Worked paragraph on why American entry was the strategic turning point: American entry on 6 April 1917 reshaped the strategic arithmetic of the war. President Woodrow Wilson's declaration of war followed three catalysts: Germany's resumption of unrestricted submarine warfare on 1 February 1917, the interception and publication of the Zimmermann Telegram in February 1917 (in which German Foreign Minister Arthur Zimmermann invited Mexico to attack the United States), and the sinking of American merchant ships in March 1917. Although American troops arrived slowly — only around 85,000 were in France by March 1918, but two million by the Armistice — the strategic effect was immediate. Germany now faced a closing window: either win before the American Expeditionary Force deployed in strength, or face defeat by attrition. Ludendorff's Spring Offensive of 21 March 1918 was the direct product of this calculation, and its failure left Germany unable to withstand the Hundred Days. American entry therefore mattered not only for the manpower delivered but for the timetable it imposed on German strategy — a timetable Ludendorff could not meet.
"America joining the war meant Germany lost. They sent lots of troops and won battles. This was the main reason." — Simple; no specific detail.
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