In the United States, where you live can affect the power of your vote. And before the era of high-tech gerrymandering, a series of U.S. Supreme Court decisions in the 1960s forced states to redraw egregiously outdated voting maps and served as an equalizing force in American democracy.

As a result of this “redistricting revolution,” Americans became more uniformly represented in their legislatures than they had in the past 50 years. The Supreme Court decisions established that the number of legislative representatives in a district or state must accurately reflect the number of people who live there.

States, some of which hadn’t redrawn their maps in more than sixty years, were subsequently forced to update their legislative districts after every census so each district had roughly equal populations. This had a huge impact on voters in the United States—at least until computer technology ushered in a new form of gerrymandering in the late 1970s.

The people behind the redistricting revolution were mostly city-dwellers who lacked equal representation with those in rural areas. “Up until that point, there was no enforceable requirement of equal-population districts redrawn after every 10 years,” says David Stebenne, a professor of history and law at The Ohio State University. “It’s not strictly speaking an outgrowth of the civil rights movement, but the people involved in this litigation can see the parallel.”

Leaders in the civil rights movement supported these cases and were aware that they would boost black voting power in the north and, hopefully, one day in the south (the redistricting revolution court cases preceded the Voting Rights Act of 1965). Stebenne thinks members of the court who decided the redistricting revolution cases were “mindful of the link” to the civil rights movement, too. (Chief Justice Earl Warren wrote the majority opinion in Brown v. Board of Education, and presided over one of the more activist courts in U.S. history.)

Before 1900, states had regularly updated their districts without being told. But after the 1900 census, many states stopped redrawing their maps in order to keep political power in the hands of those who already had it: white, rural, native-born Americans.

As more people moved from rural areas to cities and suburbs over the next 60 years, rural residents gained disproportionate political power over the rest of the state. This was the case in southern states like Tennessee, as well as northern states like Illinois. In the north, the failure to redraw districts ensured that black Americans who moved to cities during the Great Migration, as well as immigrants from southern and eastern Europe, would have less political power when they got there.

These uneven districts often favored one party over another—Republicans in the north, Democrats in the south—and this political dimension was one reason the Supreme Court preferred not to intervene in redistricting cases like Colegrove v. Green in 1946. But less than 20 years later, the court had changed, and the majority of the justices saw it as an issue of equal protection under the 14th Amendment.

In 1962, the court ruled in Baker v. Carr that Tennessee had to redraw its uneven districts, which the state had not updated since the 1900 census. The next year, the court ruled in Gray v. Sanders that states must have a “one person, one vote” standard in statewide elections—something that seems like it should be obvious, but evidently was not.

Then in 1964, the court followed this up with two major, game-changing decisions. In Reynolds v. Sims, the court ruled that all state legislative districts must have roughly equal populations. And in Wesberry v. Sanders, it ruled that states must regularly adjust their federal congressional districts so that each of the 435 members in the House of Representatives represents roughly the same number of people. This meant states would gain or lose members as their populations shifted. (The court ruled the U.S. Senate could continue giving every state two members regardless of population because it was a unique institution; but no state legislatures could operate this way.)

It took awhile for states to redraw their districts, but once they did, the change was significant. “You could argue that most even-handed drawing took place from the mid-’60s through late ‘70s,” Stebenne says. After that, the redistricting revolution came up against a problem none of the justices could’ve predicted—high-tech gerrymandering.

Gerrymandering has existed in some fashion ever since the founding of the United States; and though the redistricting revolution made gerrymandering more difficult, it didn’t make it impossible. By the late 1970s, Stebenne says tech firms in California had designed “sophisticated computer software that would enable people [or] parties to draw these really exotic-shaped districts that maximize partisan advantage while still preserving equal-population districts.”