Neutrality violated: Initially, the US tried to remain neutral in the conflict, but Germany disregarded American neutrality with its unrestricted submarine warfare policy, which involved sinking merchant ships without warning, even those carrying passengers. This resulted in the loss of American lives and vessels, prompting public outrage.
Zimmerman Telegram: The interception and decoding of the Zimmermann Telegram, a secret diplomatic communication from Germany to Mexico, played a significant role in swaying American public opinion. The telegram proposed an alliance between Germany and Mexico if the US entered the war. This revelation created a sense of betrayal and heightened concerns about Germany's intentions.
Lusitania Sinking: The sinking of the British passenger ship Lusitania by a German U-boat in May 1915, resulting in the deaths of over 1000 people, including 128 Americans, caused widespread indignation in the United States. The incident reinforced the sense of Germany's disregard for international law and human life.
Economic ties and loans: The United States had significant economic ties with Britain, France, and other Allied nations, providing substantial loans to support their war efforts. As the war progressed, these economic considerations became more intertwined, making the US more invested in the Allied cause.
Public support: Over time, public sentiment in the US shifted in favor of intervention, as the war was increasingly viewed as a contest between democracy and autocracy. The country's progressive movement and influential figures, like President Woodrow Wilson, advocated for supporting democratic allies and opposing the aggressive actions of Germany.