He was one of the leading socialist theoreticians of his period and, during the German occupation of Belgium during World War II, played a limited role in collaboration.

Returning to Belgium after the Reichstag fire (his books were not popular with Hitler, and de Man was always a maverick relative to others' ideologies) he became Vice President of the Belgian Labour Party (POB-BWP).

[1] The doctrine of Henri de Man intended to overcome the successive crises of capitalism by the nationalization of bank credit and an elevation of the degree of authority of the State in financial affairs, while preserving the structures of a capitalist economic system.

From a tactical point of view, marked by the crushing of the German Social Democrats by Hitler, which he attributes to the defection of the middle classes towards the NSDAP, de Man thought it necessary to move towards a rapprochement with liberal parties.

point out that it was quite unlike the New Deal, proposing not a safety net of welfare and other benefits, but an anti-democratic prescription invented by a man disillusioned with democracy and the working class.

When he proposed it on the floor of the parliament, his opponents shouted, "That is pure fascism" in a debate that caused de Man to suffer a stroke on the spot, and paralyzed him for almost three months.

After the "capitulation" of the Belgian Army in 1940, he issued a manifesto to POB-BWP members, welcoming the German occupation as a field of neutralist action during the war: "For the working classes and for socialism, this collapse of a decrepit world, far from being a disaster, is a deliverance.

Henri de Man had been depressed and immobilized in Switzerland for years, prevented from returning to Belgium by the threat of trial and imprisonment for treason.