A century ago today, the United States Congress, acting on the request of President Woodrow Wilson, declared war on Imperial Germany. Four days before, on the evening of April 2, the president addressed a joint session of Congress, asking for war. The subsequent vote was hardly close, with the House voting 373 to 50 in favor, while the Senate’s tally of 82 to six was even more lopsided.
This was the most important foreign policy decision made by Washington in the entire 20th century, since by entering the First World War—called the Great War at the time—the United States determined the outcome of that momentous and horrible conflict and thereby set Europe on a course for an even more terrible war to come.
None of that could be known at the time, of course. Reluctantly, President Wilson finally decided to enter the war—after successfully running for reelection in 1916 on a peace platform—when Berlin’s conduct became intolerable, leading to American deaths. Like the college professor he was, Wilson hoped for peace and considered the Great War to be a by-product of Europe’s decrepit and illiberal empires, to which the president and his fellow American progressives felt morally superior.
Wilson did not enter the war lightly. How could he, once word of the appalling losses of 1916 reached America? Nightmares like Verdun and the Somme, where millions of Europeans killed and maimed each other without changing much of anything strategically, meant no sensible person could welcome more such slaughter.
That said, Wilson was sympathetic to the Allies, Britain and France especially, viewing them as the last bastion of resistance to authoritarian Teutonic hegemony over Europe. To say nothing of the fact that the British and French were heavily dependent on American supplies and money to stay in the war. By early 1917, London and Paris, which had tapped out their own treasuries, needed help from New York banks to keep fighting. It’s no exaggeration to state that American finance needed an Allied victory to recoup its massive loans which sustained the war effort.
Fortunately for Wilson, Berlin proved a highly cooperative adversary. Viewing American neutrality as a fiction, Germany decided to restart unrestricted submarine warfare at the beginning of February 1917. Their previous use of their navy’s submarine arm in 1915 against merchant ships headed across the Atlantic resulted in significant losses for the Allies—but also terrible press for Berlin.
In particular, the German sinking of the British liner Lusitania in May 1915 off the coast of Ireland, which killed 1,198 of her passengers and crew, among them 128 Americans, made Berlin realize the political cost of her submarine strategy. As a result, the Germans backed off—for a while.
However, by the beginning of 1917, Germany was clearly losing, thanks to the British naval blockade which was starving her war economy of the raw materials needed to sustain the conflict. It was also slowing starving the German population, too. Restarting unrestricted submarine warfare looked like Berlin’s only way to fight back, and to prevail in the Great War.
Germany’s military leadership fully expected that this move would push America into the conflict, officially. They simply didn’t care. In military terms, the U.S. Army was small and out-of-date, hardly more than a constabulary designed to subjugate Native Americans; it was not a serious fighting force in German eyes.
Berlin correctly assessed that it would take at least a year for America to assemble a real army and get it to Europe in numbers worth talking about. German generals planned to win the war by then, so it hardly mattered. In the end, they nearly pulled it off—but not quite.
German submarines starting sinking America ships on the high seas again, without warning, and the expected public outrage followed. Washington broke off diplomatic relations with Berlin as the crisis mounted through February 1917. Nevertheless, America remained a divided country. Although many citizens wanted to enter the conflict to save the world from “Hun barbarism,” a quasi-religious crusade that was pushed by the politically powerful mainline Protestant churches, there were plenty of dissenters.
Millions of Americans of German descent, some notably prominent, had no stomach for a fight against their ancestral homeland, no matter how much Berlin misbehaved, while plenty of Irish-Americans would fight to protect the British Empire under no circumstances whatsoever. Wilson therefore faced a formidable obstacle in early 1917.
Fortunately for the president, the most important intelligence coup of the 20th century came to his rescue at exactly the right moment. Unbeknownst to Washington, British naval intelligence had secretly been reading German diplomatic and military codes since the opening months of the war. This gave London an enormous advantage in every aspect of the conflict, above all with enforcing the naval blockade against Germany.
On January 16, 1917, Royal Navy codebreakers intercepted and began decrypting a message between Berlin and the German mission in Mexico City. By the next day, it was obvious they had a bombshell on their hands. The message, sent by Arthur Zimmermann, the German foreign minister, ordered his ambassador to Mexico to prepare for war with the United States, and to get Mexico in the conflict too—on Germany’s side. It read:
We intend to begin on the first of February unrestricted submarine warfare. We shall endeavor in spite of this to keep the United States of America neutral. In the event of this not succeeding, we will make Mexico a proposal of alliance on the following basis: make war together, make peace together, generous financial support and an understanding on our part that Mexico is to reconquer the lost territory in Texas, New Mexico, and Arizona. The settlement in detail is left to you.
Top British officials understood that something like a miracle had dropped in their laps. Even the most antiwar Americans would take unkindly to the loss of several states—Mexico’s “lost provinces”—to their greedy southern neighbor. The message had to be shared with Washington—but how?
London faced two problems. First, the Royal Navy adamantly refused to let the Americans know about their code-breaking prowess, which was a closely guarded secret even inside the British government. Then there was the important matter of exactly how British codebreakers got their hands on the Zimmermann Telegram.
At the beginning of the war, Britain severed all of Germany’s undersea telegraph cables, cutting Berlin off from the world. Her only means of communication with her diplomatic missions abroad was via radio, which was easily intercepted. German diplomats pleaded with Washington that they now had no means to conduct the peace negotiations they claimed to want so badly. In a moment of liberal broad-mindedness, President Wilson permitted Berlin to use American government cables to send their diplomatic messages worldwide. In other words, the Royal Navy intercepted the Zimmermann Telegram because they were reading secret U.S. State Department cable traffic.
That obviously could not be shared with the Americans, so the head of Royal Navy intelligence, Admiral Reginald “Blinker” Hall, devised a brilliant deception scheme. He dispatched a British agent to steal a copy of the very same encrypted German message from a Mexican telegraph office—which was the version to be shared with Washington.
Hall presented that message to the American embassy in London on February 19, which soon forwarded it on to the White House. Outraged, Wilson decided to share the Zimmerman Telegram with the public, which he did on February 28. The sensational news took America by storm, inflaming anti-German (and anti-Mexican) passions. Overnight, only the most diehard isolationists remained unmoved by Wilson’s plea to enter the Great War on the Allied side.
It is commonly said that our April 6, 1917 declaration of war on Germany ended America’s isolation from the world, which is hardly true. Our first foray into global adventurism, the 1898 war against Spain, was militarily a middling affair, hardly more than down-punching against the decrepit Spanish empire, yet it won America colonies from the Philippines over to Puerto Rico.
Nevertheless, American entry into the Great War was a much more consequential decision, since it made German victory impossible and thereby decided the conflict’s outcome. With our seemingly limitless manpower and material resources, the United States represented an unreachable enemy for Berlin. To make matters worse, Germany’s plan to win the war by mid-1918 failed dismally. Their big spring offensives inflicted sharp blows on the British and the French, bringing German forces close to Paris for the first time since 1914—yet ultimately petered out. After massive losses of men and equipment, Berlin could no longer make good.
By the middle of the summer, German forces on the Western Front were in slow retreat as American troops poured into France in staggering numbers. Untried in battle yet eager for the fight, the American Expeditionary Force only participated in one major campaign on the Western Front, the Meuse-Argonne Offensive, which kicked off in late September and ran until the armistice on November 11, 1918. In 47 days of brutal fighting, the AEF proved its mettle, pushing the defeated Germans back all along the front, but at a frightful cost of 122,000 casualties, including 26,000 dead Americans. Although nearly forgotten by the public, the Meuse-Argonne remains the bloodiest battle in American history.
It’s no exaggeration to state that American intervention in the Great War led directly to Germany’s defeat. Whether that was ultimately a good thing remains a more open question than many realize. While Imperial Germany wasn’t exactly a liberal democracy, neither was it a murderous dictatorship—and it bore no resemblance to the terrible Nazi regime which came to power in 1933, riding the coattails of resentments and economic deprivation caused by Germany defeat in 1918.
Wilson’s harsh policies toward Austria-Hungary, Germany’s ailing ally, proved even more disastrous. The president despised the retrograde and too-Catholic Habsburg Monarchy, and its dissolution at the end of the Great War was a direct result of Wilson’s desire to dismantle that ancient empire. Of course, that collapse led to bloodshed and chaos across Central Europe and the Balkans, which raged for decades—and in some cases still hasn’t completely ended.
Counterfactual history is a hazardous game, but it’s easy to imagine a very different Europe coming to pass without American intervention in April 1917. Some sort of peace would eventually have emerged out of the Great War stalemate that was broken by the Americans. It would have been a German-dominated Europe, but we have that now anyway. Importantly, it would not have given prominence to murderous madmen such as Bolsheviks and Fascists, while Adolf Hitler might have died, penniless and forgotten, as the aspiring artist-manqué he really was.
It bears noting that American codebreakers only realized in the late 1930s that they had been had by Blinker Hall and his cunning spy-deception, two decades too late to matter, when an even more terrible conflict was looming on the horizon.
John Schindler is a security expert and former National Security Agency analyst and counterintelligence officer. A specialist in espionage and terrorism, he’s also been a Navy officer and a War College professor. He’s published four books and is on Twitter at @20committee.