 Author of numerous books and articles, his reputation was established by his book "Het fascisme en de nieuwe vrijheid" (Fascism and the New Freedom) which was published in 1939, shortly before the outbreak of the Second World War.De Kadt's early political career was shaped, in part, by the influence of Rosa Luxemburg.He joined the Dutch Communist Party, soon only to become disenchanted with it and, especially, with the political developments in the Soviet Union.