(A) The League of Nations requested help.
(B) The Maine was blown up in Havana Harbor.
(C) Nazi tyranny threatened Western democracy.
(D) ** German submarines sank United States merchant ships.
EXPLANATIONS BELOW
Concept note-1: -On April 2, President Wilson asked Congress to declare war against Germany specifically citing Germany’s renewed submarine policy as “a war against mankind. It is a war against all nations.” He also spoke about German spying inside the U.S. and the treachery of the Zimmermann Telegram.
Concept note-2: -Americans entered the war in 1917 by declaring war on Germany. This was due to the attack on Lusitania, the unrestricted submarine warfare on American ships heading to Britain, and Germany encouraging Mexico to attack the USA.