 Similarly, liberalism draws upon the work of Kant and Rousseau, with the work of the former often being cited as the first elaboration of democratic peace theory.Though contemporary human rights is considerably different from the type of rights envisioned under natural law, Francisco de Vitoria, Hugo Grotius and John Locke offered the first accounts of universal entitlement to certain rights on the basis of common humanity.In the 20th century, in addition to contemporary theories of liberal internationalism, Marxism has been a foundation of international relations.