On April 2, 1917, a pivotal moment in American history unfolded as President Woodrow Wilson addressed a joint session of Congress, advocating for a declaration of war against Germany. This decision marked the United States’ entry into World War I, a conflict that had already engulfed Europe for years. Wilson’s address highlighted Germany’s breach of its commitment to restrict submarine warfare in the Atlantic and Mediterranean, alongside its clandestine attempts to forge an alliance with Mexico against the U.S., as the compelling reasons for this momentous declaration. Two days later, both the U.S. Senate and the House of Representatives officially declared war on Germany, followed by a declaration of war against Germany’s ally, Austria-Hungary, on December 7, 1917. But what were the underlying factors that propelled the United States, initially committed to neutrality, into the throes of World War I?
Germany’s aggressive resumption of submarine attacks in 1917 on both passenger and merchant vessels emerged as the foremost catalyst for President Wilson’s decision to lead the United States into the global conflict. This escalation directly violated the earlier “Sussex pledge.” This pledge was a result of the 1916 sinking of the Sussex, an unarmed French vessel in the English Channel. Following this incident, President Wilson had firmly warned Germany, threatening to sever diplomatic ties unless the German government ceased attacks on all passenger ships and ensured the safety of crews on enemy merchant ships before any assault. The German government conceded to these demands on May 4, 1916, formalizing the agreement as the “Sussex pledge.”
However, by January 1917, Germany’s strategic calculations shifted dramatically. At a crucial wartime conference that month, the German Navy’s representatives successfully persuaded the military leadership and Kaiser Wilhelm II that a renewed campaign of unrestricted submarine warfare held the key to defeating Great Britain within a mere five months. German policymakers reasoned that the “Sussex pledge” could be disregarded, arguing that the United States had forfeited its neutral status by actively supplying munitions and financial aid to the Allied nations. Furthermore, Germany perceived the U.S. as having compromised its neutrality by tacitly accepting the Allied blockade against Germany.
Despite strong opposition from German Chancellor Theobald von Bethmann-Hollweg, who cautioned that resuming submarine warfare would inevitably draw the United States into the war on the side of the Allies and ultimately lead to Germany’s defeat, the German government proceeded with its perilous strategy. They resolved to reinstate unrestricted submarine attacks on all Allied and neutral shipping within designated war zones. Their gamble was based on the belief that German U-boats could cripple the Allied powers before the United States could effectively mobilize and deploy troops to Europe. Consequently, on January 31, 1917, Count Johann von Bernstorff, the German Ambassador to the United States, delivered a formal note to U.S. Secretary of State Robert Lansing, officially announcing Germany’s intention to recommence unrestricted submarine warfare the following day.
World War I Trenches in France: This image depicts the harsh realities of trench warfare during World War I, highlighting the conditions that American soldiers would soon face after the U.S. entered the conflict.
President Wilson was deeply unsettled by this declaration. On February 3, he addressed Congress to announce the severance of diplomatic relations with Germany. Yet, he stopped short of requesting a war declaration. Wilson remained hesitant, unconvinced that the American public was ready for war without compelling evidence of Germany’s intent to attack U.S. ships without warning. He maintained a glimmer of hope for negotiation, contingent on Germany’s submarines refraining from targeting U.S. vessels. However, throughout February and March 1917, German submarines relentlessly attacked and sank multiple U.S. ships, resulting in the tragic deaths of numerous American seamen and civilians and further inflaming public sentiment.
In response to these escalating attacks, President Wilson sought authorization from Congress on February 26 to arm U.S. merchant ships with U.S. Navy personnel and weaponry. Although this measure was likely to pass a vote, a group of anti-war Senators successfully employed a filibuster, effectively stalling the legislation for the remainder of the congressional session. Frustrated by this legislative roadblock, President Wilson resorted to issuing an executive order to arm U.S. merchant ships, invoking an antiquated anti-piracy law to justify his action.
Simultaneously, as Wilson grappled with the submarine crisis, he also had to confront another critical issue: Germany’s clandestine attempts to establish a secret alliance with Mexico. On January 19, 1917, British naval intelligence intercepted and decrypted a telegram dispatched by German Foreign Minister Arthur Zimmermann to the German Ambassador in Mexico City. This communication, known as the “Zimmermann Telegram,” revealed Germany’s promise to assist Mexico in reclaiming territories ceded to the United States following the Mexican-American War, specifically Texas, New Mexico, and Arizona. In exchange for this support, Germany sought Mexican allegiance in the unfolding global conflict.
Theobald von Bethmann-Hollweg, German Chancellor: A portrait of the German Chancellor who opposed the resumption of unrestricted submarine warfare, understanding its risks of drawing the US into World War I.
Initially, British intelligence withheld the Zimmermann Telegram from U.S. officials to protect their code-breaking operations from German detection. However, following Germany’s resumption of unrestricted submarine warfare in February, the British government recognized the telegram’s potential to sway U.S. public and official opinion toward joining the war effort. Consequently, the British discreetly passed the intercepted telegram to President Wilson on February 24, and the explosive news dominated the U.S. press the following week, further galvanizing public opinion against Germany.
Despite the sensational revelations of the Zimmermann Telegram, President Wilson still hesitated to request a declaration of war immediately. It wasn’t until March 20 that he convened a Cabinet meeting to formally discuss the matter—nearly a month after he had first received the telegram. The precise motivations behind Wilson’s ultimate decision to embrace war in 1917 remain a subject of ongoing debate among historians. This is particularly considered in light of his earlier resolve to avoid war in 1915, even after the sinking of British passenger liners Lusitania and Arabic, which resulted in the deaths of 131 U.S. citizens.
The Zimmermann Telegram: A copy of the intercepted and decrypted Zimmermann Telegram, a key piece of evidence that revealed Germany’s intentions and influenced the US decision to join World War I.
Nevertheless, by 1917, the persistent German submarine attacks on U.S. merchant and passenger ships, coupled with the ominous implications of the “Zimmermann Telegram” and its veiled threat of a German-backed attack on the United States, significantly swayed U.S. public sentiment in favor of war. Furthermore, international law stipulated that the deployment of U.S. naval personnel on civilian ships to safeguard them from German submarines was, in itself, considered an act of war against Germany. Ultimately, Germany’s actions conveyed a clear message: they were not interested in pursuing a peaceful resolution to the conflict. These converging factors collectively propelled President Wilson to seek a declaration of war against Germany from Congress. Congress, recognizing the gravity of the situation and the mounting pressures, acceded to Wilson’s request, formally declaring war on Germany and ushering the United States into the global conflict of World War I.
