1. Unrestricted Submarine Warfare: Germany's resumption of unrestricted submarine warfare, targeting merchant ships without warning, posed a direct threat to American lives, vessels, and trade. The sinking of the passenger ship RMS Lusitania in 1915, resulting in the loss of 128 American lives, caused public outrage and helped turn the tide of public opinion in favor of intervention.
2. Violation of Neutral Rights: Germany's disregard for neutral rights and its violation of international law further strained relations with the United States. The interception and publication of the Zimmermann Telegram, which revealed Germany's attempts to incite Mexico against the US, added to the growing sense of grievance.
3. Economic Ties and Trade: The United States had significant financial investments and trade ties with the Allied Powers (France, Britain, and Russia). The increasing trade deficit with the Allies, the prospect of lucrative war contracts, and the potential loss of postwar markets if the Allies were defeated, influenced American economic interests toward supporting their cause.
4. Idealistic Motives: Woodrow Wilson, the president of the United States, believed that the war was a struggle between democracy and autocracy, and he strongly advocated for the promotion of democracy and peace in the world. He saw an opportunity to shape the postwar world order and establish a more just and stable global system.
5. Domestic Political Pressure: Pro-intervention groups, such as the American Defense Society and the Navy League, actively lobbied for US involvement in the war. Preparedness parades and campaigns contributed to a growing sense of national patriotism and readiness for military action.
6. Influence of Public Opinion: The American media played a significant role in shaping public opinion. Newspapers, magazines, and motion pictures portrayed the conflict as a moral struggle against tyranny, emphasizing the humanitarian causes and the need to defend democracy and freedom.
Ultimately, it was a combination of economic interests, violation of neutral rights, moral concerns, and public pressure that solidified American support for the Allied cause and led to the US declaration of war on Germany in April 1917.