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Cartoon of a man holding a bomb exploding that says "Zimmerman Note" on it

The Zimmerman Telegram in 1917

This pop-up case is part of the series: U.S. History Series


British intelligence has decoded a secret German telegram to Mexico that proposes an alliance against the United States and shares Germany’s plans to resume submarine warfare against U.S. shipping in the coming month. How should the United States respond?

Students will understand that the decision to enter World War I involved prioritizing short- and long-term threats at home and abroad.

Students will understand that the increasingly global nature of World War I made it difficult for the United States to remain neutral as the war went on.

The Situation

By its third year, World War I had taken millions of lives in Europe and throughout the world. The United States, however, remained neutral, unwilling to commit its resources or personnel to a foreign war. Even so, it maintained trade with the Allies (France, Russia, and the United Kingdom), supporting them with arms and food exports, to the great advantage of U.S. industries. Between 1914 and 1916, U.S. trade with the Allies tripled to $3 billion annually. As U.S. ships overwhelmingly composed Allied supply lines, however, they became a target. The German navy adopted a policy of unrestricted submarine warfare, sinking any ships found approaching British waters, including neutral vessels. This policy was widely considered a violation of international law and resulted in the deaths of hundreds of Americans, including the 128 killed in the 1915 sinking of the passenger liner Lusitania. Germany halted attacks on U.S. ships after this incident, but the American public was enraged, and debate over the merits of neutrality grew louder.

On one hand, neutrality allowed the United States to trade while reserving its own resources and keeping personnel out of harm’s way. Entry into the war would require a massive mobilization of both people and industries, as the United States lacked the military resources and personnel needed to commit ground troops abroad. Some Americans saw the war in Europe as too remote to pose sufficient threat to the United States to justify the costs of war. Though they found the shipping attacks egregious, many observers doubted that Germany could launch a significant attack on the U.S. mainland. On the other hand, some Americans contended that Germany’s aggression could not be ignored. After the sinking of the Lusitania, many policymakers argued that German attacks constituted violations of American neutrality and necessitated war, while others saw the war as offering opportunities to promote democracy worldwide and prevent future wars. U.S. businesses and banks, who had loaned vast sums to the Allies, risked enormous loss if the Allies were defeated.

With the war expanding, policymakers began to wonder how much longer neutrality would even remain an option. Growing tensions with Mexico, also a neutral country, underscored this danger. Sporadic border clashes and U.S. meddling in the Mexican revolution that had persisted since 1910 left the neighbors with a mistrustful relationship. An ocean separated the United States from the war in Europe, but U.S. policymakers feared the possibility that Mexico could ally with Germany and the other Central Powers to bring the war to U.S. soil. Not only could the Central Powers try to leverage Mexico to tie down American troops and equipment that otherwise would have been sent to Europe, but they could also trigger a conflict that directly threatened the U.S. mainland.

Decision Point: Set in February 1917

British intelligence has just shared an intercepted telegram, written in January by German Foreign Minister Arthur Zimmerman to the Mexican government, revealing that Germany intends to resume unrestricted submarine warfare on the United States starting in February. The telegram further proposes an alliance with Mexico, promising that, if the United States enters the war, Germany will support a Mexican campaign to reclaim the territory it lost to the United States in the 1830s and 1840s. President Woodrow Wilson has convened his cabinet to decide whether and how to maintain neutrality, or whether it is time to enter the war. Cabinet members will need to evaluate the threat posed by the telegram to U.S. shipping and the risks of hostility with Mexico, weighing these against the considerable risks and costs of entering the war.

Cabinet members should consider the following policy options:

  • Strengthen defensive measures but remain neutral, including by reinforcing the U.S.-Mexico border and arming U.S. merchant ships crossing the Atlantic.This option could protect U.S. interests at home and abroad temporarily but would not altogether deter aggression, leaving the United States to face many more attacks. This option requires the fewest resources, focuses primarily on domestic U.S. interests, maintains lucrative U.S. shipping, and does nothing to incite an attack from Mexico. 

  • Take offensive actions short of war by launching small-scale retaliations at German submarines or calculated acts of sabotage in Mexico.This option allows the United States to seek retribution for German aggression and protect U.S. investments without requiring full mobilization for war. It does not guarantee U.S. entry into the war but risks escalating tensions that could draw the United States into a more costly exchange.

  • Declare war on Germany and enter the war on the side of the Allied powers. Committing troops to Europe would require full military mobilization: diverting industries to wartime production and boosting U.S. military capacity through a draft. It would put U.S. personnel at risk and require significant resources, but, if successful in the war, the United States could diminish Germany’s threat, expand democracy worldwide, and shorten the length of the war. This option could risk inciting an attack from Mexico, although mass mobilization could also deter potential Mexican aggression.

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