I know your question is rhetorical, but I can't pass up a chance to respond.
The reasons for the US entry into WWI are admittedly murky, but the "official line" is:
President Woodrow Wilson declared a U.S. policy of absolute neutrality on the same day Britain declared war, 4 August 1914, an official stance that would last until 1917 when Germany's policy of unrestricted submarine warfare - which seriously threatened America's commercial shipping (which was in any event almost entirely directed towards the Allies led by Britain and France) - forced the U.S. to finally enter the war on 6 April 1917.
Like WWII, we tried to stay out of Europe's mess (or what has been called "A Family Affair", since many of the European leaders involved were related to each other)...and much to Wilson's credit, we did keep to our own business for the first 3 years of this conflict.
Now, you can debate that our "reasons" for entering both WWI and WWII were flimsy at best, (I for one am absolutely convinced that Roosevelt knew we were going to be attacked, but needed an "excuse" to get us involved) but let me remind you that Germany was years ahead of us in Jet Propulsion, Rocketry and development of a Nuclear Arsenal.
Imagining an "unimaginable scenario", Nazi Germany could have been the only country with "the bomb" and the means to deliver it to any point on the globe...
Churchill said it best, "Never in the field of human conflict was so much owed by so many to so few."