I am a pupil of the great Erik von Kuehnelt-Leddihn, since the 1970s. I know extensively of the National Socialist German Workers Party as a Socialist movement. Von Kuehnelt-Leddihn was an Austrian Catholic nobleman who correctly saw raw democracy verse Republic as a threat to individual liberty, he also wrote extensively on the Leftism of the NSDAP, one of his great works was entitled Leftism, viz:
Leftism, From de Sade and Marx to Hitler and Marcuse. New Rochelle, New York: Arlington House Publishers, 1974.
I strongly recommend this book.
By the way, modern Islamic terrorism, with roots to the North West Frontier Province of India (now Pakistan) and the Khilfat movement, has strong roots in Leftism, viz Baathists and the revival movement of the Ottoman Empire among the brotherhoods such as Muslim Brotherhood and others, they are socialists as well and riff with “dirty Capitalist Jews” propaganda. Usama Bin (Osama bin Laden) had many Socialist books.
Thank you for that recommendation.