rentiers incurred no sacrifice for their earnings, and their savings did not lead to productive investments unless aggregate demand in the economy was sufficiently high. "I see, therefore, the rentier aspect of capitalism as a transitional phase which will disappear when it has done its work." Post-war economic expansion and emerging ecological concerns The economic expansion following World War II took place while mainstream economics largely neglected the importance of natural resources and environmental constraints in the development. Addressing this discrepancy, ecological concerns emerged in academia around 1970. Later on, these concerns developed into the formation of ecological economics as an academic subdiscipline in economics. Post-war economic expansion and the neglect of mainstream economics After the ravages of World War II, the industrialised part of the world experienced almost three decades of unprecedented and prolonged economic expansion. This expansion — known today as the Post–World War II economic expansion — was brought about by international financial stability, low oil prices and ever increasing labour productivity in manufacturing. During the era, all the advanced countries who founded — or later joined — the OECD enjoyed robust and sustained growth rates as well as full employment. In the 1970s, the expansion ended with the 1973 oil crisis, resulting in the 1973–75 recession and the collapse of the Bretton Woods monetary system. Throughout this era, mainstream economics — dominated by both neoclassical economics and Keynesian economics — developed theories and models where natural resources and environmental constraints were neglected. Conservation issues related specifically to agriculture and forestry were left to specialists in the subdiscipline of environmental economics at the margins of the mainstream. As the theoretical framework of neoclassical economics — namely general equilibrium theory — was uncritically adopted and maintained by even environmental economics, this subdiscipline was rendered largely unable to consider important issues of concern to environmental policy. In the years around 1970, the widening discrepancy between an ever-growing world economy on the one hand, and a mainstream economics discipline not taking into account the importance of natural resources and environmental constraints on the other hand, was finally addressed — indeed, challenged — in academia by a few unorthodox economists and researchers. Emerging ecological concerns During the short period of time from 1966 to 1972, four works were published addressing the importance of natural resources and the environment to human society: In his 1966 philosophical-minded essay on The Economics of the