For economy more Americans lived in the cities than on farms. The nation’s total wealth more than doubled and economic growth put Americans into new consumer society. As far as culture...the 1920’s were roaring and cultural women became more sexually free. The 19th Amendment allowed women to vote.And millions of women worked on white collar jobs.
The main thing that the AEF, doughboys, and harlem hellfighters (369th regiment), have all in common is that they were part of the "American Expeditionary Forces," who were sent to Europe in 1917.
Starting even before 1914, the means that a European country use to build up a strong military would be recruiting men and training them, as well as increasing the budget for the military in order to purchase for their weapons. For example, some countries built or bought ships to scare the other countries and to demonstrate power.
