The voting law that became a major turning point in black Americans’ struggle for equal rights and political power is now outdated, the Supreme Court says.

Whether that’s a marker of racial progress or proof of backsliding will be hotly debated. But neither side denies that remarkable changes were wrought through the nearly half-century-old Voting Rights Act.

As the issue moves to Congress, a look at the law’s history:

15th Amendment

The right to vote was supposed to be guaranteed when the 15th Amendment was added to the U.S. Constitution after the Civil War. Freed slaves began voting and even winning office, but former Confederate states came up with tactics to evade the amendment. Tactics such as literacy tests, poll taxes and other discriminatory laws, as well as intimidation and violence, continued for decades. In 1940, only 3 percent of eligible blacks in the South were registered to vote, according to the American Civil Liberties Union.

The march from Selma

Activists who tried to help blacks register in the South in the 1960s were met with violence. The fatal shooting of a demonstrator by a law officer in Alabama inspired the idea of a march to the state capital on March 7, 1965. Hundreds of marchers on their way to Montgomery were clubbed and tear-gassed by state troopers at the Edmund Pettus Bridge near Selma. TV news cameras captured what became known as “Bloody Sunday,” and protesters across the country rallied in support of the marchers. President Lyndon Johnson seized the momentum to propel the Voting Rights Act through Congress, signing it into law on Aug. 6, 1965.

Voting rights act

The law outlawed racial discrimination against voters in local, state and federal elections. Some entire states, as well as counties in other states, were subjected to special federal enforcement, based on a formula used to weigh their record on voting rights. They had to get approval in advance before they could make even minor changes to voting laws, such as moving polling places. The enforcement provisions were originally seen as emergency measures that might be allowed to expire in 1970 if no longer needed. But lawmakers extended the provisions in 1970, 1975 and 1982. In 2006, Congress voted overwhelmingly to keep them another 25 years.

Tuesday’s ruling

The Supreme Court’s 5-4 decision effectively halts enforcement of the Voting Rights Act, unless Congress updates it. The court said Congress has failed to adjust the law to reflect decades of strides toward racial equality. The United States now has a black president; a black justice sits on the Supreme Court. And 48 years after “Bloody Sunday,” Selma is governed by a black mayor, Chief Justice John Roberts noted, writing for the court’s conservative majority. The Supreme Court decision means that a host of state and local laws in covered jurisdictions now can take effect without Justice Department approval. Prominent among those are voter identification laws in Alabama and Mississippi.

What’s next

President Barack Obama said the Supreme Court decision was a disappointing setback, and called on Congress to act to rectify the situation. But the Republican-led House and Democratic-led Senate find few points of agreement these days. And Congress did nothing in response to a 2009 Supreme Court ruling that warned lawmakers that the Voting Rights Act’s enforcement formula needed to be updated. Unless Congress acts, there will be no deterrent to changes that would undermine voting rights, such as redrawing districts to dilute the power of minority voters. Voters can still use lawsuits to challenge such changes.