The correct answer to this open question is the following.
The factor that played in the United state enjoying economic prosperity during the roaring '20s was that the country did not incur in big amounts of debt during World War 1, as Europeans countries did. Indeed, the United States loaned big sums of money to Western European countries to support the war effort. That is why the United States could live a period of economic prospeity in those years called "the Roaring 1920s," a period in which people had money or could buy using credit all the things they needed or they liked.
