Nearly 14 million immigrants entered the United States from 2000 to 2010, and over one million persons were naturalized as U.S. citizens in 2008. The per-country limit applies the same maximum on the number of visas to all countries regardless of their population and has therefore had the effect of significantly restricting immigration of persons born in populous nations such as Mexico, China, India, and the Philippines—the leading countries of origin for legally admitted immigrants to the United States in 2013; nevertheless, China, India, and Mexico were the leading countries of origin for immigrants overall to the United States in 2013, regardless of legal status, according to a U.S. Census Bureau study.