This document discusses the nature and development of modern sociological theories from the 1920s to 1960s. It notes that classical sociological theories became foundational due to how subsequent modern theories engaged with them. Major political and social changes like the world wars, rise of fascism/communism, and decolonization stimulated the emergence of new sociological perspectives like functionalism and conflict theory to understand issues like democracy, economic development, and state-society relations. The professionalization of American sociology in universities led to distinct schools of thought and a focus on empirical research methods.