How was the consumerism and prosperity of the 1950's a direct result of the preceding twenty years ?
The consumerism and prosperity of the 1950s were (we can argue) a direct result of the previous twenty years because those years had involved deprivation and war.
On the one hand, the prosperity of the 1950s came largely out of World War II. The war was good for the American economy. It got the US out of the Great Depression. It created many new kinds of technologies that came to be used for consumer purposes. It also led to the GI Bill, which helped to make the American economy stronger by giving many more people a college education.
On the other hand, the consumerism of the 1950s came out of the deprivation of the Great Depression and the war. Between 1929 and the late 1940s, Americans had had to live without much in the way of material goods, relatively speaking. Americans had had things bad for so long that they were extremely eager to have material comforts once prosperity returned. Therefore, when the prosperity of the 1950s arrived, they were very interested in making sure that they had material goods like cars, TVs, and single-family homes.
In these ways, the previous two decades contributed greatly to the prosperity and consumerism of the 1950s.