Here’s a simple (perhaps simplistic) point made by nuclear historian James Mahaffey (from his Atomic Awakening):
At the end of World War II, the United States had the only uranium enrichment plant in the world, turning out U-235 in any desired concentration in quantities limited only by the amount of material loaded into the front-end. The availability of this one facility would influence the path of nuclear-power development in the United States, make it different from the course taken in any other country with nuclear ambitions, and permanently affect worldwide nuclear design.
Mahaffy, James. 2009. Atomic Awakening: A New Look at the History and Future of Nuclear Power. Pegasus, New York, pp. 146-147.
Of course, Mahaffey’s sparky assertion is both correct and just the starting point for historical analysis. America’s wealth of enriched uranium did make it easy for that nation to look at power reactor designs that use LEU (lightly enriched uranium), but many, many designs, not all LEU-based, were explored. Yes, other countries either could not get LEU in the early years or did not want to buy or beg from the United States. But many other factors complicate the historical outcome of the design battles – LEU versus natural uranium – as they were played out in any particular place. Key individuals also played a part.