This was reflected in Foster's early book "The Theory of Monopoly Capitalism" and the coedited volume (with Henryk Szlajfer), "The Faltering Economy: The Problem of Accumulation under Monopoly Capitalism". In the late 1980s, Foster turned toward issues of ecology. He focused on the relationship between the global environmental crisis and the crisis in the capitalist economy, while stressing the imperative for a sustainable, socialist alternative. During this period he published "The Vulnerable Planet: A Short Economic History of the Environment"; his article "Marx's Theory of Metabolic Rift" in the "American Journal of Sociology"; and "Marx's Ecology: Materialism and Nature". His reinterpretation of Marx on ecology introduced the concept of "metabolic rift" and was widely influential. This work led to his receiving the Distinguished Contribution Award of the American Sociological Association's Environment and Technology section. "Marx's Ecology" itself received the book award from the ASA's Section on Marxist Sociology. This work was soon followed up by his book "Ecology Against Capitalism", which focused on the critique of capitalist economics from the standpoint of the environment. As editor of "Monthly Review", Foster returned to his earlier work on the political economy of capitalism, but with a renewed focus on the role of U.S. foreign policy following September 2001. His 2006 book "Naked Imperialism", along with frequent editorials in the pages of "Monthly Review", attempted to account for the growing U.S. military role in the world and the shift toward a more visible, aggressive global projection. Additionally, Foster has worked to expand Sweezy and Baran’s theory of monopoly capital in light of the current financially led phase of capitalism, which he terms "monopoly-finance Capital." In this context he has written several books on the financialization of capitalism and financial crisis of 2007–08. "Critique of Intelligent Design", Foster’s book co-authored with Brett Clark and Richard York, is a continuation of his research on materialist philosophy and the relationship between ancient Greek philosopher Epicurus and Karl Marx. Drawing on his ecological work, particularly "Marx’s Ecology", Foster defends historical materialism as fundamental to a rational, scientific worldview, against proponents of Intelligent Design and other non-materialist ideologies.