This immigration changed the character of American and build it up, industrially, culturally and spiritually. That was possible largely because of generally tolerant immigration laws, except for anti-Asian laws. The Constitution gave to Congress the power to establish a uniform naturalization law. Later, the 14th Amendment protected the rights of all children born in the U.S. In 1875 the U.S. Supreme Court ruled that states may not pass there own immigration laws, that under the Constitution, including the 14th Amendment, immigration is the province of the federal government. Some of the few limits to immigration were laws excluding lunatics, the illiterate,infection disease carriers and anarchists. Immigration through points of entry, like Ellis island, was usually easy, but becoming a naturalized citizen was a much longer process. The border with Mexico was fluid, with many families having lived, worked and owned land for generations both in Mexico and in the Southwest to the point that it may have been unclear to many of them which country they were citizens of. It was only in the 1920's, after World War I, that the U.S. initiated strict immigration quotas, the Emergency Quota Act. Similar, more complex plans followed. It was largely after this that anything like "illegal" or "undocumented" immigration emerged, largely from the countries with the lowest quotas or in the Southwest from those who continued to go back and forth across the border. during the 1930's depression millions were "repatriated" across the border to Mexico, regardless of their documentation status.
The Know Nothings, none as the American Party, emerged in the 1850's as the first of many anti-immigration and anti-Catholic organizations. Another secret Society, the American Protective Association was founded in 1887 by Protestants to oppose Catholics and immigration. Various sub-groups, fraternal organizations and splinter groups came out of it. The Klu Klux Klan revived in the 1920's as a nativist and pro-Jim Crow organization. Anti-Chinese racism during this period also created Chinese exclusion laws.