After the Second World War, and particularly after the quick success of the United States-financed Marshall Plan in helping to rebuild the European economies, several economists who had been directly involved either in the Marshall Plan or with institutions such as the United Nations and the World Bank, turned their attention to the question of economic development of less-developed regions. Among these early pioneers of development thinking were the Finnish economist Ragnar Nurkse, the Austrian economist Paul Rosenstein-Rodan, the German-born economist Albert Hirschman, the West Indian and later Nobel Laureate economist, Sir Arthur Lewis, and the American economic historian Walt Whitman Rostow. Only Lewis remained outside of the policy-making institutions in the late 1940s and early 1950s, but by 1957 he too was employed by the UN.