It was not until the passage of the Immigration and Nationality Act of 1952 that the racial and gender restrictions for naturalization were explicitly abolished. However, the act still contained restrictions regarding who was eligible for US citizenship, and retained a national quota system which limited the number of visas given to immigrants based on their national origin, to be fixed "at a rate of one-sixth of one percent of each nationality's population in the United States in 1920". It was not until the passage of the Immigration and Nationality Act of 1965 that these immigration quota systems were drastically altered in favor of a less discriminatory system.