The Voting Rights Act, passed by the U.S. Congress and signed into law by President Lyndon B. Johnson on August 6, 1965, suspended literacy tests and nationally prohibited abridgment of the right to vote based on race or color. It also authorized the Office of the Attorney General to examine voting practices in areas where discrimination was suspected. Plans to demonstrate compliance required preclearance from the Justice Department. The act also found that poll taxes were preventing African Americans from voting, leading to a Supreme Court finding in 1966 that they were illegal. Though the measure was aimed at reversing southern discrimination against African Americans, it applied equally to all immigrants who had become naturalized citizens. As Nathan Glazer observed in Clamor at the Gates, the Civil Rights Act of 1964 and the Voting Rights Act of the following year went hand in hand with the nonracial Immigration and Nationality Act of 1965 to represent a broadly national consensus—at least outside the South—that equality should not have a racial component (see RACISM). Prior to World War II (1941–45), there was practically no registration of minority voters in the South. In 1940, only 3 percent of otherwise eligible black voters were registered. The federal government had been ineffectual in its haphazard attempts to undermine the disenfranchisement of blacks that was routinely being practiced in the South through the use of intimidation and various economic and literacy tests, mainly because previous Supreme Court decisions had limited congressional authority in enforcing amendments passed during the Civil War (1861–65) but also because of the strength of the southern voting bloc in the Senate. By 1957, a modest civil rights measure was passed, enabling the attorney general to seek injunctions against violation of the Fifteenth Amendment guarantee that “the right of citizens of the United States to vote shall not be denied or abridged by the United States or by any State on account of race, color, or previous condition of servitude.” Beginning in the early 1960s, acts of violence, including the murder of voting-rights activists in Philadelphia, Mississippi, gained national attention. The attack by state troopers on peaceful protesters in Selma, Alabama, on March 7, 1965, convinced President Johnson that special legislation was necessary to overcome southern resistance to the implementation of equal voting rights, despite the protections already offered in the Fifteenth Amendment. According to Minnesota senator Walter Mondale, a Democrat, the “outrage” in Selma made “passage of legislation to guarantee southern Negroes the right to vote an absolute imperative for Congress.” Between 1965 and 1969, on several occasions the Supreme Court upheld the constitutionality of the preclearance requirement in Section 5, arguing that “case-bycase litigation was inadequate to combat wide-spread and persistent discrimination in voting, because of the inordinate amount of time and energy required to overcome the obstructionist tactics invariably encountered in these lawsuits.” The Voting Rights Act was amended in 1970, 1975, and 1982, further strengthening protection of voting rights. By the end of the 1960s, registration of black voters in the Deep South had increased to more than 60 percent, and an increasing number of African Americans were being elected, mainly at local and county levels.