Paul Krugman has clarified the microeconomic underpinnings of both spatial economic agglomerations and regional imbalances at national and international levels. He has achieved this with a series of remarkably original papers and books that succeed in combining imperfect competition, increasing returns, and transportation costs in new and powerful ways. Yet, not everything was brand new in New Economic Geography. To be precise, several disparate pieces of high-quality work were available in urban economics and location theory. Our purpose in this paper is to shed new light on economic geography through the lenses of these two fields of economics and regional science.
The paper provides quite a list of these predecessors, and although the paper does not highlight them too much, they include his paper in 1988 in RSUE that pretty much fully covered what is in the 1991 paper by Krugman, "A monopolistic competition model of spatial agglomeration: a differentiated product approach." The extensive literature he cites includes two important papers in 1980 and 1982 by him with H. Ogawa, as well as highlighting the foundational work in the 1940s and 1950s by the "Father of Regional Science," the still-living at 90 years old, Walter Isard, also one of the founders of "Peace Economics."