
Alex S. answered 04/05/19
MA in Sociology with 3+ Years of Teaching Experience
It only takes one person to establish a theory, especially in the social sciences. Theory is but a framework used in formulating hypotheses, not the end result of research. Marx, Weber, Durkheim, Wallerstein, Foucault, Baudrillard, etc. are all well-respected theorists and did not collaborate with anyone else (unless you credit Engels for assisting Marx - but he is mostly a forgotten man).
In contemporary academia, peers and professors will push a narrative that you need multiple citations for a theoretical work, but remember that the classical theorists that contemporary theorists cite did not concern themselves with peer review. If you want to publish in today's climate, you need an introduction in which you perform a peer reviewed literature review. However, in the main body of your theoretical work, you should not need to cite anyone unless you are referencing and interacting with their work.
I hope this helps!