Final answer:
President Woodrow Wilson justified U.S. entry into World War I by emphasizing the need to "make the world safe for democracy" and to support international collective security through the League of Nations.
Step-by-step explanation:
President Woodrow Wilson's main justification for the entry of the United States into World War I was to make the world safe for democracy. This reflected Wilson's vision for a peaceful postwar world governed by the principles of self-determination and collective security, as embodied by the proposed League of Nations. Brought into sharp focus with the German U-boat campaign threatening neutral nations and international trade, Wilson's declaration was also a response to events such as the sinking of the Lusitania and the interception of the Zimmermann Telegram, which proposed a military alliance between Germany and Mexico against the United States.
Despite his initial reluctance, Wilson recognized that a German victory would dangerously alter the power balance in Europe and potentially threaten democratic nations and ideals worldwide.
His commitment to the freedom of the seas and the protection of neutral rights in times of war was also a critical factor in his decision to enter the conflict. Wilson's Fourteen Points outlined his vision for a postwar world, which included the formation of the League of Nations to prevent future conflicts.