Introduction
In the dark days of early 1917, the Allied cause looked increasingly bleak. The great powers of Europe had been locked in savage combat for over two and a half years, with millions dead and no end in sight. The previous year had seen the grinding slaughters of Verdun and the Somme, where combined casualties exceeded 2 million men. But the strategic calculus changed dramatically in January 1917 with the interception of the Zimmermann Telegram. This secret German diplomatic cable, proposing an alliance with Mexico against the United States, helped propel America into World War I. The ensuing flood of Yankee troops and materiel tipped the scales and helped seal Germany‘s eventual defeat.
The State of Play in Early 1917
As 1917 dawned, the Great War was mired in bloody deadlock, especially on the Western Front. The Central Powers of Germany and Austria-Hungary battled the Entente of Britain, France, Italy and Russia in a calamitous conflict that had already claimed unprecedented millions of lives. The Battle of Verdun, waged from February to December 1916, sucked in 1.25 million men and left over 700,000 casualties.[^1] The concurrent Battle of the Somme, from July to November, was even more costly, with more than 1 million men wounded or killed.[^2]
But beneath this stalemate, the tectonic plates were shifting. Titanic offensives had exhausted both sides. Britain introduced conscription to replace its staggering manpower losses. And Russia, wracked by the early spasms of revolution, edged toward exiting the war altogether. The departure of Russia would free some 50 German divisions – more than a million men – from the Eastern Front for redeployment in the West.[^3] A German offensive to break the deadlock and seize decisive victory before the Americans arrived in force looked increasingly likely.
Outraging American Public Opinion
Against this backdrop, Germany made a fateful decision. On January 9, 1917, it announced that its submarines would resume unrestricted warfare, sinking merchant ships without warning, even those from neutral countries. To German military planners, this was a calculated risk to strangle British supply lines before America could effectively intervene. But it outraged American public opinion, which still smarted from the sinking of the passenger liner Lusitania in 1915. President Woodrow Wilson severed diplomatic relations with Berlin in protest.
This alone did not bring American entry, as Wilson still clung to neutrality. But on top of this provocation landed the Zimmermann Telegram in late February. British intelligence intercepted and decrypted a secret cable from German Foreign Minister Arthur Zimmermann to Germany‘s ambassador in Mexico City, Heinrich von Eckardt. Incredibly, Zimmermann instructed Eckardt that if the U.S. entered the war, he should propose a military alliance with Mexico. Germany would provide generous financial support and the promise of regaining territory lost to the U.S. in Texas, New Mexico, and Arizona.[^4]
The British cunningly handed this bombshell to the American government, which shared it with the press. The American public reacted with disbelief and then fury at this blatant foreign intrigue aimed at dismembering the nation. Coupled with Germany‘s resumption of unrestricted U-boat attacks, it made American involvement a foregone conclusion. On April 2, Wilson asked Congress for a declaration of war, arguing that "the world must be made safe for democracy."[^5] Four days later, the United States formally entered World War I.
Impact of American Economic Might
The effects of American belligerence were felt immediately in terms of economics and finance. Even before sending masses of troops, the U.S. ramped up the supply of war materiel, food, and fuel to the beleaguered Allies. American factories retooled to churn out staggering quantities of shells, guns, ships, vehicles, and other supplies. By the end of the war, for instance, the U.S. had manufactured 1.5 million rifles, 18.5 million pairs of boots, 53 million gas masks, and astonishing 7.5 billion rounds of ammunition.[^6]
Crucially, the U.S. also increasingly financed the Allied war effort. Even as a neutral, America had provided significant loans, with $2.3 billion to Britain and $1.6 billion to France by April 1917.[^7] These sums ballooned to over $10 billion by the Armistice. Such economic aid was instrumental in keeping the Allies afloat, as their economies buckled under the strain of total war. J.P. Morgan, Jr., head of the Wall Street banking dynasty, remarked that before American entry, the Allies had been "financially done up" and nearing bankruptcy.[^8]
American Boots on the Ground
Still, it was the arrival of masses of fresh American troops that had the most palpable effect. Wilson ordered the induction of over 2.8 million men under the Selective Service Act, which allowed the eventual deployment of over 2 million "doughboys" to France.[^9] Though slow to arrive in 1917, the ranks of the American Expeditionary Forces (AEF) swelled in the new year. Some 10,000 men per day poured into France through the summer of 1918.[^10]
While inexperienced, American units were well-equipped, thoroughly trained, and flush with vigor. French Prime Minister Georges Clemenceau remarked to U.S. General John Pershing that "the Americans soldier well because you are fresh and you believe."[^11] They first saw significant combat at the Battle of Cantigny in May 1918. Though a small engagement involving only 4,000 doughboys, it demonstrated American competence and bolstered Allied morale.[^12]
The following month, U.S. Marines etched their legend in blood and valor in the Battle of Belleau Wood. Dug-in German machine gun nests and artillery decimated the Marines as they advanced across open wheat fields. But the dogged Americans prevailed, capturing the woods after 20 days of brutal fighting at the cost of nearly 10,000 casualties.[^13] When Paris was threatened by the final German spring offensives, U.S. troops played a key role in blunting the advance at the Battle of Château-Thierry, plugging gaps in the Allied line.[^14]
Turning the Tide: The Hundred Days Offensive
By August 1918, the strategic balance had shifted. The arrival of over 1.2 million Americans allowed the Allies to match German numbers.[^15] The AEF undertook its first offensive at the Battle of Saint-Mihiel in September, where Pershing assembled over 550,000 men and 2,900 artillery pieces. In a stunning success, American forces recovered the Saint-Mihiel salient in a mere 4 days.[^16]
This was a prelude to the massive Meuse-Argonne Offensive, the largest and bloodiest American operation of the war. Involving over a million U.S. troops, it was part of the wider Allied Hundred Days Offensive that decisively pushed the Germans back in the fall of 1918.[^17] The scale of the assault was staggering, as Pershing committed over 2,700 artillery pieces, 380 tanks, and 840 aircraft in support.[^18] After 6 weeks of ferocious combat, with over 120,000 American casualties, the doughboys cracked the vaunted Hindenburg Line, breaking any hope of German resistance.[^19]
Aftermath: An American Peace
Germany‘s strategic dilemma was inescapable. Its army was being ground down by the day, while a flood of Americans continued to pour in. Morale collapsed, with the shocking realization that Germany could not win, especially after Bulgaria, the Ottoman Empire, and Austria-Hungary sued for peace in October.[^20] Domestic unrest flared in Germany, with mutinies, strikes, and calls for the Kaiser‘s abdication. On November 11, 1918, the guns fell silent with the signing of the Armistice.
American intervention had proved decisive in the endgame of World War I. The millions of fresh troops and huge quantities of supplies from across the Atlantic broke the back of German resistance. Historian David Stevenson estimated that absent American involvement, the war would likely have dragged on until at least 1919 or 1920, and possibly ended in stalemate.[^21]
President Wilson arrived at the Paris Peace Conference with grand visions for a new world order, based on his iconic Fourteen Points. These included self-determination, disarmament, freedom of the seas, and a League of Nations to settle global disputes.[^22] While Wilson‘s soaring utopianism clashed with the realpolitik of the European victors, he succeeded in establishing the League as part of the Treaty of Versailles.
Conclusion
The long-term reverberations of American intervention in World War I are still felt today. It marked the end of America‘s isolationism and its rise to superpower status on the world stage. The punitive peace imposed on Germany, and resentment over Wilson‘s unfulfilled promises, sowed seeds that would sprout into fascism, communism, and World War II. A century on, the Great War still echoes.
But none of it may have happened without the Zimmermann Telegram. This incredible cable shook America out of its ambivalence and onto the world stage, irrevocably and consequentially. It remains one of the most astonishing diplomatic miscalculations in history. In a war full of might-have-beens, Zimmermann‘s folly was a true fulcrum, on which the fate of nations hinged. As a historian, it‘s impossible to overstate the momentousness of the Telegram in sparking American intervention, the most transformative event in the cataclysm of World War I.
[^1]: John Keegan, The First World War (New York: Knopf, 1999), 300.[^2]: William Philpott, Three Armies on the Somme: The First Battle of the Twentieth Century (New York: Knopf, 2009), 518.
[^3]: David Stevenson, Cataclysm: The First World War as Political Tragedy (New York: Basic Books, 2004), 318.
[^4]: Thomas Boghardt, The Zimmermann Telegram: Intelligence, Diplomacy, and America‘s Entry into World War I (Annapolis: Naval Institute Press, 2012), 148.
[^5]: Woodrow Wilson, "Address to Congress Requesting a Declaration of War Against Germany," April 2, 1917, in The American Presidency Project.
[^6]: Thomas Boyd, ed. World War I: A Turning Point in Modern History (New York: Knopf, 1968).
[^7]: Kathleen Burk, Britain, America and the Sinews of War, 1914-1918 (Boston: Allen & Unwin, 1985), 90.
[^8]: John Milton Cooper, Jr., Woodrow Wilson: A Biography (New York: Knopf, 2009), 381.
[^9]: Jennifer D. Keene, World War I: The American Soldier Experience (Lincoln: University of Nebraska Press, 2011), 8.
[^10]: Stevenson, Cataclysm, 318.
[^11]: Allan R. Millett, The War for Korea, 1945–1950: A House Burning (Lawrence, KS: University Press of Kansas, 2005), 7.
[^12]: Edward G. Lengel, Thunder and Flames: Americans in the Crucible of Combat, 1917-1918 (Lawrence, KS: University Press of Kansas, 2015), 128.
[^13]: Stephen L. Harris, Duffy‘s War: Fr. Francis Duffy, Wild Bill Donovan, and the Irish Fighting 69th in World War I (Washington, D.C.: Potomac Books, 2006), 265.
[^14]: Richard S. Faulkner, Pershing‘s Crusaders: The American Soldier in World War I (Lawrence: University Press of Kansas, 2017), 393.
[^15]: John S.D. Eisenhower, Yanks: The Epic Story of the American Army in World War I (New York: Free Press, 2001), 167.
[^16]: Donald Smythe, Pershing: General of the Armies (Bloomington: Indiana University Press, 1986), 190.
[^17]: David R. Woodward, Trial by Friendship: Anglo-American Relations, 1917-1918 (Lexington, KY: University Press of Kentucky, 1993), 6.
[^18]: Edward G. Lengel, To Conquer Hell: The Meuse-Argonne, 1918 (New York: Henry Holt, 2008), 77.
[^19]: Robert H. Ferrell, America‘s Deadliest Battle: Meuse-Argonne, 1918 (Lawrence: University Press of Kansas, 2007), 151.
[^20]: David Stevenson, With Our Backs to the Wall: Victory and Defeat in 1918 (Cambridge, MA: Belknap Press, 2011), 465.
[^21]: Stevenson, With Our Backs to the Wall, 545.
[^22]: John Milton Cooper, Jr., Breaking the Heart of the World: Woodrow Wilson and the Fight for the League of Nations (New York: Cambridge University Press, 2001), 13.
