On March 1, 1917, an explosive story hit the front pages of major U.S. newspapers, about a German telegram that had fallen into the hands of the American government. By then, the United States was already on its slow and inexorable path to war with Germany and, in the telegram, German Foreign Minister Arthur Zimmermann instructed his ambassador in Mexico on what to do if America failed to maintain its neutrality and joined the Allied forces.

“In the event of this not succeeding,” Zimmermann’s note read, “we 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 ambassador was also directed to urge Mexico to strike up an alliance with Japan in an eventual fight against America.

The U.S., at the time, was highly divided about international conflict. Months earlier, Woodrow Wilson had eked out the narrowest electoral win of the 20th century, save for 2000, on the strength of the re-election slogan “He Kept Us Out of War”—a reference to not only the trenches of Europe, but an ongoing civil war in Mexico.

Needless to say, news of a German plot to incite Mexico to go to war with the United States further inflamed an already contentious debate, which manifested itself in perhaps familiar ways. Following the publication of Zimmermann’s memo, some anti-interventionists, who opposed American entry into the war, immediately decried it as a forgery. “There were accusations that it was fake news, that it was a hoax,” said Christopher Capozzola, a professor of history at MIT and the author of Uncle Sam Wants You: World War I and the Making of the Modern American Citizen. “There was definitely some sense that some people believed from the beginning that it was fake, but it was confirmed very quickly.”

Despite its incendiary nature and the breadth of the news coverage of it, history remains somewhat split about the material effect that the Zimmermann Telegram had on public sentiment or America’s decision to declare war on Germany just one month later. An entry in the National Archives concludes the communique “helped draw the United States into the war and thus changed the course of history.” Others argue that the impact of the telegram on pulling America into war was nothing compared to, say, Germany’s resumption of unrestricted submarine warfare, which threatened any ship crossing the Atlantic.

“All the newspapers I looked at [from the time] … had strong opinions about the telegram, but I couldn’t find a single newspaper that changed its opinion on intervention because of the telegram,” said Thomas Boghardt, who is the senior historian at the U.S. Army Center of Military History and the author of The Zimmermann Telegram. “It might have accelerated America’s entry into the war by a few weeks, but America was on its way into the war. You could make that argument, but let’s not mistake that for a cause.”

Despite the fallout, which involved German backpedaling and Mexican disavowals, the aftershocks from the incident may have been felt more in the arena of domestic politics than international politics. “Once Wilson learns about it, he doesn’t immediately release it,” Capozzola explained. “He eventually releases it as a weapon to intervene in a congressional debate” where the telegram is used to freeze out anti-interventionist lawmakers. “It was a pretty long slow slide into the war, but after the Zimmermann Telegram, it becomes very difficult for the U.S. to think that it can make any peaceful coexistence with Germany.”

As America moves closer to its World War I centennial this spring, there are different facets of l’affaire Zimmermann that echo in a 2017 context. It’s notable that the U.S. only caught wind of Zimmermann’s note because the British had been reading all the diplomatic correspondence that passed through the American Embassy in London, which at the time also included Germany’s cables to North America. Following the discovery and decoding of Zimmermann’s proposal for a German-Mexican alliance in January 1917, Captain William Hall, who headed up the British navy’s codebreaking outfit, held onto the telegram for weeks in part so he could construct a backstory that wouldn’t tip off the neutral Americans that their ally had been spying on them. Eventually, Hall, without consulting his government, would hand the memo over to Walter Page, the U.S. ambassador in London, a maneuver that very easily could have backfired.

“Of course, he [Hall] couldn’t say, ‘Well, I’m regularly reading your mail,’” said Boghardt. “He was really a master of not only intelligence, but also of, ‘How do you tell it? When do you tell it? To whom do you tell it? How do you cover your tracks?’ He understood this game very well. This is really the beauty of the Zimmermann Telegram: It’s not only a coding and decoding story, but how you also leak something to the right outlet at the right time with the maximum effect.”

For Imperial Germany, the Mexico proposal was part of a strategy to keep the United States bogged down on its own home front, much in the way that it had sidelined Russia in the war by supporting Vladimir Lenin and the Bolsheviks in their revolution against the Russian Empire. While proposing an alliance in the likelihood of war falls within diplomatic norms, what Zimmermann failed to grasp were the political ramifications. “There really was no large influential press or public opinion or free elections there,” Boghardt explained. “They had a hard time understanding how American public opinion works and how powerful it could be. This is something that the British understood much better.”

In this way, the Zimmermann Telegram heralded a new, more sophisticated evolution in the world of intelligence. As Boghardt points out, intelligence to that point had previously been limited to espionage and the pilfering of sensitive information. “World War I is really where you have this switch, where signals intelligence—this is what the Zimmermann Telegram is—starts playing a much bigger role and people understand that you gain a lot more information by monitoring communications.” The irony is that one thing that may have hastened America’s self-described war to make the world safe for democracy was the manipulation of the public sentiments that guide democracy.