<P> In 1848, the Treaty of Guadalupe Hidalgo, concluding the Mexican War, extended U.S. citizenship to approximately 60,000 Mexican residents of the New Mexico Territory and 10,000 living in California . An additional approximate 2,500 foreign born California residents also become U.S. citizens . </P> <P> In 1849, the California Gold Rush attracted 100,000 would - be miners from the Eastern U.S., Latin America, China, Australia, and Europe . California became a state in 1850 with a population of about 90,000 . </P> <P> Between 1850 and 1930, about 5 million Germans migrated to the United States, peaking between 1881 and 1885 when a million Germans settled primarily in the Midwest . Between 1820 and 1930, 3.5 million British and 4.5 million Irish entered America . Before 1845 most Irish immigrants were Protestants . After 1845, Irish Catholics began arriving in large numbers, largely driven by the Great Famine . </P> <P> After 1880 larger steam - powered oceangoing ships replaced sailing ships, which resulted in lower fares and greater immigrant mobility . Meanwhile, farming improvements in Southern Europe and the Russian Empire created surplus labor . Young people between the ages of 15 to 30 were predominant among newcomers . This wave of migration, constituting the third episode in the history of U.S. immigration, may be better referred to as a flood of immigrants, as nearly 25 million Europeans made the long trip . Italians, Greeks, Hungarians, Poles, and others speaking Slavic languages made up the bulk of this migration. 2.5 to 4 million Jews were among them . </P>

Between 1900 and 1920 where did most of the migrants to the united states come from