It is estimated that 500,000 immigrants from 80 countries- ranging from Australia, New Zealand, Canada, Mexico, Central and South America, Russia-were processed at Angel Island; however, most of the immigrants coming through Angel Island were from China and other Asian countries, and detained for extended periods of time and faced more rigorous process to arrive at the mainland due to the passing of the Chinese Exclusion Act in 1882, which barred Chinese laborers from coming to the United States, limited immigration to those who have relatives in the U.S., and prevented Chinese immigrants from becoming naturalized citizens. After the passing of the Chinese Exclusion Act, customs service officers individually and arbitrarily implemented the law. By the first decade of the 20th century, a national system of procedures became standardized and enforcement fell on the Bureau of Immigration.