At the beginning of the 20th century the Italians were the main group entering the United states. Most Italians found unskilled work in America's cities. There were large colonies in New York, Philadelphia, Chicago, Baltimore and Detroit. From 1900 to 1910 over 2,100,00 arrived. Willing to work long hours on low wages, the Italians now began to rival the Irish for much of the unskilled work available in industrial areas. This sometimes led to hostilities breaking out between the two groups of workers. The Italians were also recruited into the garment industry and by the outbreak of the First World War had replaced the Jews as the main group in the sweated trades.

In 1919 Woodrow Wilson appointed A. Mitchell Palmeras his attorney general. Worried by the revolution that had taken place in Russia in 1917, Palmer became convinced that Communist agents were planning to overthrow the American government. Palmer recruited John Edgar Hoover as his special assistant and together they used the Espionage Act (1917) and the Sedition Act (1918) to launch a campaign against radicals and left-wing organizations.

A. Mitchell Palmer claimed that Communist agents from Russia were planning to overthrow the American government. On 7th November, 1919, the second anniversary of the Russian Revolution, over 10,000 suspected communists and anarchists were arrested in what became known as the Palmer Raids. Palmer and Hoover found no evidence of a proposed revolution but large number of these suspects were held without trial for a long time. The vast majority were eventually released but 248 other people were deported to Russia. This included a large number of Jews including Emma Goldman, Alexander Berkman and Mollie Steimer.

Persecution of Jews by the Nazis in Germany in the 1930s once again increased a desire to emigrate to the United States. Arrivals included Albert Einstein, Alfred Adler, Edward Teller, Karen Horney, Erich Fromm, Berthold Brecht, Kurt Weill and Hans Eisler.