Republican gerrymandering efforts used to focus mainly on diluting the influence of cities. Legislators could cram urban Democrats into one or two districts to preserve the surrounding districts for Republicans, or divide them among many districts in which they would be outvoted.

That hasn’t stopped. But redistricting maps approved this year show the battle lines radiating outward to the suburbs, where Republicans are trying to build levees against an increasingly Democratic and multiracial tide.

What’s striking is how thoroughly the racial diversification and leftward shift of the suburbs have changed the task for the architects of gerrymandering: The suburbs, historically used by Republicans to defend against the electoral threat of cities, are now themselves a threat.

“You used to crack the urban areas and join them to the suburbs, and now you’re having to crack the suburbs and join them to rural areas,” said Michael Li, senior counsel for the Democracy Program at the Brennan Center for Justice. “What these tactics show is that Republicans are not confident that they’re going to get white suburban voters back in anywhere near the numbers they need anytime soon, so they’re hedging their bets by treating the suburbs as enemy territory as opposed to friendly territory.”

These changes also reduce the voting power of communities of color even though those are the communities whose growth earned states like Texas new congressional seats.

Take Texas’ 13th Congressional District, which extends 450 miles from the Texas Panhandle to just outside the Dallas-Fort Worth metropolitan area, and which the Republican-controlled State Legislature redrew this year to include increasingly blue suburbs north of Dallas and Fort Worth. The district has always been Republican and will remain so; its new Democratic residents are far too few to make a difference. And dissolving them into the red — and white — seas of the Panhandle enabled Republicans to cram the rest of the Dallas-Fort Worth region’s Democrats into three districts instead of four.

Or look at the 22nd Congressional District, south of Houston. It was previously centered on Fort Bend County, which is home to Asian, Black and Latino communities and voted for President Biden. The district’s new lines encompass rural areas to the southwest, putting it out of Democratic reach after two election cycles in which a Democrat, Sri Preston Kulkarni, was competitive. Much of Fort Bend County will move into the Seventh District, already held by a Democrat.

In some cases, Republicans have ceded cities in order to shore up the suburbs. Previously, Texas legislators split Travis County — which includes Austin — among five districts, four of them red. This year, they gave Austin two Democratic districts in exchange for safe Republican seats all around it.

Republicans are also taking aim at suburbs in Georgia, where Democrats flipped two Atlanta-area House districts — the Sixth in 2018 and the Seventh in 2020 — that were once Republican strongholds. Those Democratic gains stemmed in part from political shifts among white suburbanites but also from Black, Asian and Latino population growth.

Under maps passed by Georgia’s Republican-led legislature, the bluest parts of both districts would be stuffed into the Seventh, while rural territory in northwestern Georgia would neutralize the remainder of the suburbs and make the Sixth District safely Republican.

Allison Riggs, a co-executive director and chief counsel for voting rights at the Southern Coalition for Social Justice, emphasized North Carolina. There, legislators packed urban voters into one district each in Charlotte and Raleigh, and parceled out the increasingly Democratic and decreasingly white suburbs among several.

“You know in these counties and in these areas, there are enough votes to create new opportunities for voters of color, new opportunities for Democrats,” Riggs said. “And instead they’re carved up like a pizza pie.”

Neil Makhija, the executive director of the advocacy group Indian American Impact, noted that growing Asian American communities had helped turn many suburbs blue, including in Georgia and North Carolina last year, when they voted in larger numbers than they had in previous elections.

He expressed concern about the new district lines around Dallas and Fort Worth that link suburban Indian American communities to rural counties along the Oklahoma border.

The “G.O.P. can pack or crack our communities and claim they aren’t racial gerrymandering, but instead using partisan indicators,” Makhija said, adding that his group was also closely watching redistricting in Democratic states like New York and California. “There’s no difference to us, however, because the end result is the same: We lose our voice in the process.”

In lawsuits, advocacy groups are still focusing largely on cities, where they have the strongest cases under the Voting Rights Act of 1965. It requires mapmakers to draw opportunity districts — where a racial minority group is a majority of the voting-age population — under certain conditions when demographics make it possible.

In the Texas suburbs, Latino communities are growing but are generally not large enough to create congressional opportunity districts, said Nina Perales, vice president of litigation at the Latino civil rights organization MALDEF, which is suing Texas officials for failing to draw Latino-majority districts in urban areas of Dallas-Fort Worth and Houston, as well as in South Texas.

The targets in the suburbs, she said, are more often multiracial communities where no single racial group could form a majority in a congressional district, but multiple racial groups with aligned interests and political preferences could.

But state legislative districts can be a different story.

“If an incumbent started out last decade in a district that was not majority Latino, but through the course of the decade, with the incremental growth and relative growth of communities, their district has become majority Latino — that’s when we are concerned that it could lead to the dismantling of an existing Latino-majority district,” said Thomas A. Saenz, the president and general counsel of MALDEF. And because of demographic patterns since 2010, a lot of the districts that fit that description are in the suburbs.

Maps that disadvantage people of color are not unique to Republicans. In Illinois, where Democrats are aggressively gerrymandering, Saenz cited a State Senate seat in the western suburbs of Chicago that is held by a white Democrat. That district — currently the 12th, but renumbered as the 11th on the new map — gained a Latino majority over the past decade, and legislators redrew it in a way that eliminated the majority, a move MALDEF is challenging.

But most of the gerrymandering is Republican, both because Republicans control the drawing of far more districts than Democrats do and because demographics are shifting in Democrats’ favor.

“You’re really starting to see the emergence of a new multiracial America, the politics of the future,” Li, of the Brennan Center for Justice, said. “And instead of deciding to compete for that future, Republicans have decided to kick the can down the road and try to gerrymander their way out of their problem.”