I would argue that the basis of American economic growth during this time was World War II. There are at least three reasons for saying this.
- Increase in capital. During the war, various technological advances had been achieved. One example of such advances would be the large, long-distance airplane. These sorts of advances increased the potential of the US economy. So, too, did the GI Bill. This law greatly increased the level of education and training of the US population. Both of these things increased the potential of the economy.
- Destruction of competitiors. Essentially all of the countries that could have been major competitors for the US economy were devastated by the war. This enabled US companies to expand much more than they might otherwise have been able to.
- Pent-up demand. Americans had, for at least 4 years, been making money without being able to really spend it. US productive power had been put towards war, not consumer goods, so many Americans had much more money to spend than they had in a long time (especially since the Depression preceded the war). This created a pent-up demand that exploded in the 1950s.