On the night of April 3, 1919, President Woodrow Wilson began to suffer from a violent cough. His condition quickly worsened to the point that his personal doctor, Cary Grayson, thought the president might have been poisoned. Grayson later described the long night spent at Wilson’s bedside as “one of the worst through which I have ever passed. I was able to control the spasms of coughing but his condition looked very serious.”

The culprit wasn’t poison, but the same potent strain of influenza nicknamed the “Spanish flu” that would eventually kill an estimated 20 million worldwide, including more than 600,000 in the United States. Wilson’s illness was made even worse by its timing—the president was left bedridden in the middle of the most important negotiations of his life, the Paris Peace Conference to end World War I.

Wilson came to the Paris negotiations armed with his visionary “14 Points” strategy for achieving world peace. It included calls for open and transparent peace treaties, freedom and self-determination for all European nations, disarmament, and above all the creation of a “general association of nations”—later called the League of Nations—to actively prevent all future wars.

But parts of Wilson’s post-war scheme were adamantly opposed by the other chief powers at the Paris Peace Conference, namely France and Great Britain. The French prime minister, Georges Clemenceau, openly clashed with Wilson over the level of economic punishment to inflict on the Germans. Clemenceau demanded billions in reparations for the monumental loss of French lives and property at German hands, but Wilson wanted to spare Germany such humiliation and focus instead on building up the League of Nations.

By April, the Paris negotiations were deadlocked, and that was precisely the moment when Wilson fell ill. The president was confined to his bed for five days battling a 103-degree fever and racking coughs while his doctor, Grayson, lied to the press that it was nothing more than a bad cold.

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The 1918 “Spanish” flu was notorious for aggressively attacking the respiratory system. The infection was worst in the young and previously healthy, whose immune systems could overreact to the virus and drown the lungs with fluid, killing patients in a matter of days. But for those who survived the initial onslaught, some also experienced neurological symptoms.

Even after their burning fevers subsided, flu victims described “post-influenzal manifestations,” psychotic delusions and visions that resulted from damage to the nervous system, says John Barry, author of The Great Influenza: The Story of the Deadliest Pandemic in History.

“The most comprehensive study of the 1918 pandemic noted how common neurological disorders were,” says Barry. “They were second only to the lung. This included psychosis, which was usually temporary.”

From numerous sources, it appears that Wilson suffered from similar effects during his fight with the flu at the Paris Peace Conference.

“He became paranoid,” says Barry. “Wilson thought the French had spies all around him. He was bizarrely obsessed with his furniture and his automobiles, and pretty much everyone around him noted it.”

Wilson’s chief usher, a man named Irwin Hoover, wrote later that “something queer was happening in [the president’s] mind” and that “[o]ne thing is certain: he was never the same after this little spell of sickness.”

The British prime minister, Lloyd George, came to visit Wilson during his recuperation at the Hôtel du Prince Murat and labeled Wilson’s condition a “nervous and spiritual breakdown” in the middle of the heated Paris negotiations.

Although instances of “the psychoses of influenza” had been reported by physicians as early as the Russian Flu outbreak of 1889, there was no treatment for the condition, which usually went away on its own. One hypothesis is that the neurological disorder experienced by Wilson and others was caused by brain swelling (encephalitis) associated with the flu.

When Wilson was finally well enough to re-join the Conference, he scarcely resembled the man who had fought so doggedly for his principles. The flu had weakened both his body and his mind, and Wilson simply didn’t have the strength or the will to stand his ground.

“The impact was pretty dramatic in my view,” says Barry. “Wilson had been adamant, insisting on the ‘14 Points,’ self-determination, and ‘peace without victory.’ Clemenceau had even accused him of being ‘pro-German.’ All of a sudden, Wilson caved in on all 14 points except the League of Nations, and only because Clemenceau threw him a bone.”

For Wilson’s negotiation team in Paris and his supporters back home, the Treaty of Versailles signed in June 1919 was a betrayal of everything Wilson had stood for, and set the stage for more conflict and death on European soil.

William Bullitt, an assistant to the Department of State and a loyal Wilson attaché at the Paris negotiations, immediately proffered his resignation.

“I was one of the millions who trusted confidently and implicitly in your leadership and believed that you would take nothing less than ‘a permanent peace’ based on ‘unselfish and unbiased justice,’” wrote Bullitt. “But our government has consented now to deliver the suffering peoples of the world to new oppressions, subjections, dismemberments—a new century of war.”

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The young aide’s assessment was tragically prescient. Historians agree that one of the chief causes of the rise of Adolf Hitler’s Nazi party was the humiliation and economic desperation inflicted on the German people by the Treaty of Versailles. Instead of safeguarding the world from future wars, the Treaty of Versailles helped pave the road to World War II.

Did Wilson’s illness play a significant and disruptive role in the Paris peace negotiations? Barry said it certainly had an impact.

“You can’t absolutely prove that he wouldn't have caved in on everything anyway, but if you know anything about Wilson, there’s nothing in his behavior that suggests he was a compromiser on issues like that,” says Barry. “Quite the reverse. He was insistent that it was ‘his way or the highway’ on pretty much everything.”

Returning to the United States, things only got worse for Wilson. First, Congress rejected American participation in the League of Nations, the last surviving remnant of the “14 Points,” and then Wilson suffered a debilitating stroke from which he never fully recovered.

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