Rothbard himself ultimately broke with the left, allying himself instead with the burgeoning paleoconservative movement. Drawing on the work of Rothbard during his alliance with the left and on the thought of Karl Hess, some thinkers associated with market-oriented American libertarianism came increasingly to identify with the left on a range of issues, including opposition to war, to corporate oligopolies and to state-corporate partnerships as well as an affinity for cultural liberalism. One variety of this kind of libertarianism has been a resurgent mutualism, incorporating modern economic ideas such as marginal utility theory into mutualist theory. Kevin Carson's "Studies in Mutualist Political Economy" helped to stimulate the growth of new-style mutualism, articulating a version of the labor theory of value incorporating ideas drawn from Austrian economics. Other market-oriented left-libertarians have declined to embrace mutualist views of real property while sharing the mutualist opposition to corporate hierarchies and wealth concentration. Left-libertarians have placed particular emphasis on the articulation and defense of a libertarian theory of class and class conflict, although considerable work in this area has been performed by libertarians of other persuasions.