That one researcher makes a major break-through (in this case, Goddard's liquid fuelled rocket engine) - then somebody else vastly improves on it - is nothing unique.
The fact is that, by 1940, only Germany and the Soviet Union had carried out any proper Research and Development work with rockets;
- the Red Army using these extensively in lieu of artillery, with the thinking being that rocket launching equipment did not have to be robustly constructed, as there was no recoil to absorb. Some of this weaponry proved to be extremely effective, particularly the multi-barreled launcher known as the "Stalin Organ."
- however, during those years, Germany was streets ahead of everybody else in R&D with rockets.
As pedal power correctly observes, the success of the United States space program was almost entirely dependent on Von Braun and his associates.