of the Spanish flu. People lived in isolation and fear as the influenza hit major cities. There were towns that would not let anyone enter or leave without special permission. In some places, police guards were stationed along major roads in and out of town to prevent travel.  

World War I had a dramatic impact on Americans. While the United States participated in the Great War for less than two years, over a quarter of the eligible male population fought in the war. Over four million were mobilized. While more soldiers died from disease than combat, over 50,000 men died in the fighting. This left a dramatic hole in the lives of thousands of Americans that lost their loved ones. Its impact was dramatic enough to cause Americans to push for a policy of isolation in foreign affairs that endured for two decades.

Even those that did not serve in combat were important to the war effort. The conversion to a wartime economy virtually eliminated unemployment. It was patriotic to go to work every day in war manufacturing industries. Americans were also asked to help pay for the war through higher taxes, especially for wealthy Americans. Additionally, millions of Americans purchased war bonds, often directly from their paychecks. Other sacrifices that Americans made included rationing, recycling materials, and conserving fuel and energy. The war also afforded women and African-Americans opportunities to work in industries that were not available to them in times of peace. Overall, American participation in World War I affected the entire population in profound ways.

WWI changed the United States significantly in terms of manners and morals. Many African Americans left the South for the North due to wartime jobs. Several African Americans realized that they were treated better by French soldiers than by their white officers, and they did not wish to rejoin the Jim Crow South. African Americans created their own communities in the North and began the Harlem Renaissance in the 1920s.

The war also created new roles for women. Women took on new roles in the workforce as a result of the war. Many young women sought freedom from becoming a housewife at a young age. Many became flappers, much to the consternation of their more conservative mothers. Women also agitated for the right to vote; they won this right with the Nineteenth Amendment, ratified in 1920.

WWI also led to a rift between conservative and liberal America. Conservative America did not trust the morality shown in the movies, illegal alcohol, and people leaving organized religion. Liberal America, on the other hand, placed more faith in science than religion. This led to the Scopes Monkey Trial in Dayton, Tennessee. Liberal America also supported secular films, illegal alcohol, and other mass entertainments. While some critics claimed that these demonstrated the shallowness of American culture, others claimed that these were only signs of young people wanting to have fun.

Advertisers and marketers enjoyed the boom in mass entertainments as they used celebrities to sell various goods, thus fueling an already strong consumer market from 1925 to1929. Many Americans turned to living in the cities in order to find better jobs and to enjoy more leisure activities.

The Red Scare was the United States's attempt to prevent Bolshevism at home. The United States allowed limited immigration from Eastern and Southern Europe with the Immigration Act of 1924. It did this at a time when refugees from these regions needed the United States the most. The idea was to keep anarchists and communists out of the United States. The US also passed the Volstead Act in 1919 partially as a way to look less attractive to Eastern and Southern Europeans though the courts ruled that alcohol could not be banned in religious rites. The United States also saw the regeneration of the Ku Klux Klan in the 1920s, as the group persecuted not only blacks but Jews and Catholics as well. The Wall Street bombing of 1919 was said to have been a communist plot, though it was never determined who was officially to blame.

The Red Scare and WWI drastically changed the United States domestically. While conservatives from that time period would claim that the 1920s were a period of loose morals, historians today look at it as more of a youth culture movement. People were more conscious of the consumer economy due to more expendable income as well as more free time. The Red Scare was an anti-immigrant backlash as upper-class and wealthy Americans feared Bolshevik takeover in the United States. This led to curtailing a fairly open immigration policy with hate groups chasing anyone who was not white, Anglo-Saxon, and Protestant. These trends would continue throughout the decade until the Great Depression abruptly ended what was referred to as the Roaring '20s.