The first climax of immigration, which American historians have called "the great human migration movement", occurred between 1820 and 1860, when the total number of immigrants amounted to 5 million. The immigrants came mainly from Western and Northern Europe, including about 2 million Irish, about 1.7 million Germans, and a large number of African slaves who had been trafficked to the United States. There were also a few immigrants from Asia, mainly Chinese who came to the United States to seek gold.

The second climax of immigration was from 1861 to 1880, when about 5 million immigrants came to the United States. After the end of the Civil War, the U.S. saw the peak of industrialization and a strong demand for labor. In order to attract European immigrants to the United States, in 1864, President Abraham Lincoln lobbied Congress to pass the Encouragement of Alien Immigration Act. Secretary of State Seward even issued a circular to U.S. diplomats in Europe, asking them to treat attracting European immigrants as a top diplomatic priority. In order to recruit skilled workers from Europe to work in the U.S., some companies also organized recruitment missions to Europe. They placed advertisements in many European newspapers and issued pamphlets depicting the attractive prospects of the United States for Europeans who wished to emigrate. Some companies also provided the necessary travel expenses for Europeans who wished to immigrate to the United States.

The third climax was from 1881 to 1920, when immigration jumped to 23.5 million. The peak of immigration was in 1907, when it reached 1.285 million. During this period, the U.S. government enacted several pieces of legislation to restrict European immigration and exclude Asian immigrants. While the growth of "old immigrants" from northwestern European countries such as Britain, Germany and Sweden was limited, the growth of "new immigrants" from southeastern European countries such as Italy and Russia was rapid.

As a result of these three waves of immigration, the total population of the United States exceeded 100 million for the first time in 1920. During the 100-year period from 1820 to 1920, the number of immigrants accounted for more than 20% of the annual growth of the U.S. population. These three waves of immigrants in the history of the United States not only had a profound impact on the formation of the national character of the United States of America, but also made the United States in just over a hundred years to rise rapidly, replacing the United Kingdom as the world's number one economic power, and for the future to become a world superpower to lay the foundation. It can be said that the wave of immigrants forged the strength of the United States.