From 1913 to 1921 the President of the United States was Thomas Woodrow Wilson, he kept the United States neutral during the first years of the war. After increasing pressure, the United States declared war on Germany on April 6, 1917. Although the US entered the conflict militarily in 1917, it had participated financially since 1915, issuing war funding, especially to France and England.
The United States won the war, but they also had other advantages. The war was not fought in America, so they did not have to rebuild infrastructures and there were not so many deaths. Many other states had to rebuild their cities due to the bombardments. America, thanks to their advantages, became the world leaders for the first time, overtaking England.
The Immigration Act of 1924, was a United States federal law that prevented immigration from Asia, set quotas on the number of immigrants from the Eastern hemisphere, and provided funding and an enforcement mechanism to carry out the longstanding ban on other immigrants.
The 1924 act took the place of earlier acts to effectively ban all immigration from Asia and set a total immigration quota of 165,000 for countries outside the Western Hemisphere, an 80% reduction from the average before World War I.
According to the US Department of State's Office of the Historian, the purpose of the act was "to preserve the ideal of U.S. homogeneity."
Congressional opposition was minimal.
Americans in the 1920s began to be very intolerant of everything that was not American and wanted to limit interactions between the US and abroad.
The act reduced total immigration from 357,803 between 1923 and 1924 to 164,667 between 1924 and 1925.