-Central Powers won WWI
In this scenario United States never entered the war, which lead to Entente's surrender.
-The Axis won WWII
In this scenario Germany and Japan developed nuclear weapon before United States, Washington D.C. and London get nuked, and the Allies surrendered.
-Soviet Union "won" the Cold War
In this scenario it was United States who experienced economic stagnation, and collapsed during late 20th century, while Soviet Union survived until present-day.
So, which scenario that you think would lead to "the worst possible world"...?