<P> Nearly all population growth up to 1830 was by internal increase; around 98% of the population was native - born . By 1850, this shifted to about 90% native - born . The first significant Catholic immigration started in the mid-1840s, shifting the population from about 95% Protestant down to about 90% by 1850 . </P> <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>

When did open immigration end in the us