Within sociology there have been several system theories, differing from one another in the extent to which, for example, human agency, creativity, and entrepreneurship are assumed to play a role in system formation and reformation; conflict and struggle are taken into account; power and stratification are part and parcel of the theory; structural change and transformation – and more generally, historically developments – are taken into account and explained. What the various system theories have in common is a systematic concern with complex and varied interconnections and interdependencies of social life. Complexity has been a central concept for many working in the systems perspective. The tradition is characterized to a great extent by a burning ambition and hope to provide a unifying language and conceptual framework for all the social sciences.
Tom R. Burns (2006) "System Theories" in: George Ritzer ed. The Encyclopedia of Sociology, Blackwell Publishing.