The Second World War turned industrial capital outwards in the United States and the scientific and technological changes in the post-war period led to the expansion of American private capital investment particularly in the Third World countries. The private sector in the United States became a vital sector for the expansion of national interest in American international economic relations in the post-Second World War period as couched in the Marshall Plan (1948-52). The expansion of American foreign capital investment coincided with a favourable domestic environment of operation in the host countries. Third World economies were deficient in their developmental processes from the 1950s and needed foreign capital investment to stimulate their economic growth. For these reasons, they created liberal investment legislations and signed investment agreements favourable to foreign capital investments for industrialisation. This paper sets out to examine Nigeria’s industrial policies, the American government’s disposition to her private sector’s operation in international investment environment, and the growth of American entrepreneurship in the Nigerian economy between 1950 and 1966.