In the United States, at the urging of President Lyndon B. Johnson, Congress passed the Immigration and Nationality Act of 1965 (also known as the Hart-Celler Act), which abolished national quotas for immigrants and replaced it with a system that admits a fixed number of persons per year based in qualities such as skills and the need for refuge. During the nineteenth and early twentieth centuries, most immigrants to the United States had come from Europe, but by the late 1990s and early 2000s, Asia and Latin America became the top sources of immigrants to the nation.