The key to the emergence of development economics, split off from the 
economics of developed countries, in the 1950s or thereabouts is surely the 
collapse of empires and the creation of very many new, poor, underdeveloped 
countries, hence a demand for policy advice, training, etc.

The ideological function of the division between developed and 
underdeveloped countries was in part to differentiate the product of the 
development economists who could claim that underdeveloped countries were 
different and hence needed the services of the new-fangled development 
economists and not the old-style mainstream economists. Also it served to 
allow them to advocate central planning and the like, which would not have 
been acceptable in developed countries (or, specifically, the USA). (This 
paragraph is a bit flippant - there is a lot of interest to be said about 
development economics as a phenomenon of decolonization, but no space to 
say it here.)

Tony Brewer ([log in to unmask])