 "The Biology of War" was praised by Romain Rolland, who became a friend of Nicolai.In 1922 he emigrated to South America where he worked and taught in Argentina, Physiology Department, School of Medicine, University of Cordoba and later Chile.In the 1930s he wrote "Das Natzenbuch" (A Natural History of National Socialist Movement and of Nationalism in General), in which he denounced nationalism as "one of the greatest, possibly greatest danger to the further development of the human race".