Why would America not intervening in the First World War mean no Communism in Russia (or China)?
And why would it mean no nuclear weapons?
The decision to send Lenin to Russia, (remember, the Original Russian revolution was not communist. When Lenin got there, he turned it into a communist revolution.) was made after the US announced it was entering the war on the side of the British.
I know post hoc ergo propter hoc is not perfect logic, but it seems accurate in this particular case.
And why would it mean no nuclear weapons?
No German loss in WWI, no Hitler. No Hitler, no mass persecution of the Jews. Szilard remains in Germany, as do a whole host of other important scientists that pushed for and developed this technology.
No Szilard and Einstein in the US, no push to create the Manhattan project.
Very likely the very wost things of the 20th century would have been avoided.
Some sort of drub-induced bizzaro-world butterfly effect?