As far as I know, the starting point was the foundation of the "field
office" in Paris in 1924. Rockefeller organized the funding of LSE etc.
by this office. Fellowships might have started earlier. But the social
sciences became object of the Rockefeller Foundation not before 1918.
For details see: Craver, Earlene: Patronage and the Directions of
Research in Economics: The Rockefeller Foundation in Europe 1924-1938.
In: Minerva 24 (1986), S.205-222. Craver mentions a total of 500
Fellowships between 1924 and 1934, the share of economics met 35
percent.
Jan-Otmar Hesse