Constructivism is often presented as an alternative to the two leading theories of international relations, realism and liberalism, but some maintain that it is not necessarily inconsistent with one or both. Wendt shares some key assumptions with leading realist and neorealist scholars, such as the existence of anarchy and the centrality of states in the international system. However, Wendt renders anarchy in cultural rather than materialist terms; he also offers a sophisticated theoretical defense of the state-as-actor assumption in international relations theory. This is a contentious issue within segments of the IR community as some constructivists challenge Wendt on some of these assumptions (see, for example, exchanges in "Review of International Studies", vol. 30, 2004). It has been argued that progress in IR theory will be achieved when Realism and Constructivism can be aligned or even synthesized. An early example of such synthesis was Jennifer Sterling-Folker’s analysis of the United States’ international monetary policy following the Bretton Woods system. Sterling-Folker argued that the U.S. shift towards unilateralism is partially accounted for by realism’s emphasis of an anarchic system, but constructivism helps to account for important factors from the domestic or second level of analysis.