World War I, a conflict that engulfed Europe from 1914, initially saw the United States maintain a position of neutrality. However, this stance shifted dramatically, culminating in America’s declaration of war against Germany in April 1917. Understanding why America joined WW1 requires examining a series of pivotal events and evolving political sentiments that ultimately drew the nation into the global conflict.
Germany’s decision to resume unrestricted submarine warfare in early 1917 stands as the primary catalyst for the United States’ entry into World War I. Prior to this, in March 1916, the sinking of the French passenger vessel Sussex prompted President Woodrow Wilson to demand that Germany halt attacks on passenger ships and allow crews of merchant vessels to evacuate before attacks. This ultimatum resulted in the “Sussex pledge,” where Germany agreed to these conditions.
By January 1917, the German military, particularly the Navy, convinced Kaiser Wilhelm II that unrestricted submarine warfare could cripple Great Britain within months, effectively ending the war in Germany’s favor. They reasoned that the United States had already compromised its neutrality by supplying the Allied nations with munitions and financial aid and had acquiesced to the Allied blockade against Germany. Therefore, German policymakers decided to disregard the “Sussex pledge.”
Despite warnings from German Chancellor Theobald von Bethmann-Hollweg, who feared that such a move would inevitably bring the United States into the war, the German government proceeded. On January 31, 1917, Germany informed the United States of its intent to resume unrestricted submarine warfare the following day. This meant German U-boats would target all ships, including those from neutral countries like America, within designated war zones.
President Wilson was taken aback by this announcement. On February 3, he addressed Congress, announcing the severance of diplomatic ties with Germany. However, he stopped short of requesting a war declaration, uncertain if public opinion was ready for war without concrete evidence of direct German aggression against American ships. Wilson still hoped Germany might reconsider. But in February and March 1917, German submarines sank multiple U.S. vessels, resulting in American deaths.
Following these attacks, Wilson sought Congressional authorization to arm U.S. merchant ships. While likely to pass, anti-war senators blocked the measure. Undeterred, President Wilson, invoking an anti-piracy law, authorized the arming of merchant ships by executive order.
Parallel to the submarine crisis, the Zimmermann Telegram emerged as another significant factor pushing America towards war. On January 19, 1917, British intelligence intercepted and decrypted a telegram from German Foreign Minister Arthur Zimmermann to the German Ambassador in Mexico City. This “Zimmermann Telegram” proposed a secret alliance between Germany and Mexico. Germany pledged to help Mexico reclaim territories lost to the United States in the Mexican-American War, including Texas, New Mexico, and Arizona, in exchange for Mexican support in the war against the U.S. should America enter the conflict.
Initially, Britain hesitated to reveal the telegram, fearing it would expose their code-breaking capabilities. However, with Germany’s resumption of unrestricted submarine warfare, the British saw an opportunity to sway U.S. public and political opinion towards intervention. They presented the Zimmermann Telegram to President Wilson on February 24, and the American press widely reported the story the following week.
Despite the outrage sparked by the Zimmermann Telegram, Wilson remained hesitant to declare war. He convened his Cabinet on March 20 to discuss the matter, nearly a month after receiving the telegram. Historians continue to debate the precise weight of different factors in Wilson’s ultimate decision, particularly considering his earlier efforts to maintain neutrality after the Lusitania and Arabic sinkings in 1915.
However, by 1917, the combination of relentless submarine attacks on American ships and the provocative Zimmermann Telegram significantly shifted public sentiment in the United States. The idea of armed neutrality became untenable, and international law itself suggested that arming civilian ships with naval personnel was akin to an act of war. Germany’s actions signaled a clear unwillingness to pursue a peaceful resolution. These converging factors led President Wilson to request a declaration of war from Congress against Germany, a request that Congress granted on April 6, 1917, marking America’s official entry into World War I.
