<em>The United States was drawn into World War with because of Germany’s invasion, the sinking of the Lusitania and the Zimmerman's note.
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On May 7, 1915, the German Army sank the RS Lusitania, as part of the hostilities during World War I. The sinking was part of the German attack to the British submarine because the British established a naval blockage to the navy of Germany. This action, the German invasion and the Zimmerman's note, where the Germans promised help to Mexico, were the reasons why the United State entered World War I.
With the Truman Doctrine, President Harry S. Truman established that the United States would provide political, military and economic assistance to all democratic nations under threat from external or internal authoritarian forces. Truman asked Congress to support the Greek Government against the Communists.
