The main factor that caused President Woodrow Wilson to bring the United States into World War I was Germany's policy of unrestricted submarine warfare, which violated international law and threatened American lives and interests. Germany's strategy of sinking merchant ships without warning, including those carrying American passengers, sparked outrage in the United States and made it difficult for Wilson to maintain neutrality.
Here's a more detailed explanation:
Sinking of the Lusitania:
On May 7, 1915, a German submarine torpedoed the British passenger liner RMS Lusitania off the coast of Ireland, resulting in the deaths of over 1,200 people, including more than 100 Americans. The sinking of the Lusitania enraged Americans and increased pressure on Wilson to take action against Germany.
Zimmermann Telegram:
In early 1917, the British intercepted and decoded a telegram sent by the German Foreign Secretary, Arthur Zimmermann, to the German Ambassador in Mexico. The telegram proposed an alliance between Germany and Mexico in the event of war between the United States and Germany. This revelation further convinced Wilson that Germany's actions were hostile towards American interests.
Sussex Pledge:
After the sinking of the Lusitania, Germany had pledged not to sink unarmed merchant vessels without warning. However, in March 1916, a German submarine violated this pledge by sinking the French passenger ship Sussex, injuring several Americans on board. This incident eroded any remaining trust in Germany's assurances.
Declaration of War:
In response to Germany's continued attacks on merchant ships and the revelation of the Zimmermann Telegram, President Wilson asked Congress to declare war on Germany on April 2, 1917. The United States officially entered World War I on April 6, 1917.