Personally I see the US as the turning point in WWI. Without the US on either side the war is anyone's guess.
In WWI, what possible countries could of joined the Central Powers? The US should be possible, if Roosevelt is elected instead of Wilson, the Germans don't send the Zimmerman telegram, and don't attack our ships. Italy should of been in the Central Powers in the war, since they were in the Triple Alliance. And with the US in the Central Powers Central America falls in line as well.
But besides the US & Italy (& UK, Russia, France, Portugal, & Japan) what countries could be members could of joined the Central Powers in the war? Could the Central Powers gotten more Balkan countries, Belgium, China, & Brazil? And of countries that didn't join WWI OTL who could of, such as Persia, Argentina, & Scandinavian countries? And what would be the results of such a central power victory?
My guess would be a division of Africa between the Ottoman, German, & Italian empires, full independence of India, Ireland, Bahamas, & Australia, & annexation of Canada, Newfoundland, & Bermuda by the US. France becomes the Germany of this timeline, as the blame of the war is entirely put on France.