Regarding Rothbard’s Betrayal of the Old Right, David Gorden writes:
“Things weren’t always like this. In the years before World War II, American conservatives opposed global crusading. The Old Right opposed the New Deal and favored the traditional American policy of not getting involved in foreign wars.”
There was also a british empire that controlled the trade routes, currency, and laws of exchange. There were multiple powers preventing the spread of world communism. At the end of WWII none of those countries existed.
So, as much as I understand that the USA became less isolationist, it did so not out of conviction, but of fear.
And I am not, in retrospect, sure that they were wrong to do so.