After the First World War broke out, the United States adopted a policy of neutrality at first. The public opinion was not in a mood favorable to participation in a distant war fought by selfish European powers. So, president Woodrow Wilson would have had a very hard time trying to get Congress pass a declaration of war in 1914. It was only after the sinking of the British liner Lusitania in May 1915 by a German U-boat and the loss of 128 American lives that Americans started to change their mood and supported the Allied cause against Germany. The US finally entered WWI in 1917.
Almost all men age 18-25 who are U.S. citizens or are immigrants living in the U.S. are required to be registered with Selective Service. U.S. law calls for citizens to register within 30 days of turning 18 and immigrants to register within 30 days of arriving in the U.S.
