Chinese immigration in the nineteenth century was a fundamental part of the creation of the American immigration legal system. The well-established coolie trade sent Chinese laborers across the world. With the instability generated by the Opium Wars and civil unrest, Chinese immigrants particularly from the Guangdong region, started migrating to the United States. Some migrated by choice, others were "shanghaied" -- kidnapped and forced into labor -- or trafficked. Whatever the cause, these migrants arrived at the shores of Gum Saan (gold mountain) following the discovery of gold in 1848.
These early Chinese immigrants faced harsh violence and discrimination. Hundreds of Chinatowns were burned as immigrants were pushed out and rejected by white Americans who saw Chinese as "unassimilable" and "alien." Starting with the 1875 Page Act and later with the more well-known 1882 Chinese Exclusion Act, the United States made the landmark decision to restrict immigration on the basis of race. One of the most famous cases involved Wong Kim Ark, the son of a Chinese immigrant, who was denied entry when he tried to return to the United States. His case resulted in the establishment of "birthright citizenship" which grants anyone born in the United States citizenship.
For an interesting timeline related to Asian American history, check out A Different Asian American Timeline, created by the ChangeLab.
Angel Island Immigration Station Foundation, originally from Him Mark Lai, Genny Lim and Judy Yung: Island: Poetry and History of Chinese Immigrants on Angel Island, 1910-1940, 2nd edition (Seattle: University of Washington Press, 2014).