The last decade hasn’t been kind to majority-black congressional districts across the country.

While the black population nationally ticked up 12 percent in the just-released Census numbers, eight of the top 10 majority-black districts across the country actually experienced population loss, losing an average of more than 10 percent of their black population, according to a review of Census data by The Fix.

Many of these districts lost voters of other races too, and are now in need of significant expansion during this year’s redistricting process.

The population loss is really more of a migration. The black population is moving from the major metropolitan areas – where most of these districts are – and into the suburbs. In fact, of the 15 districts with the greatest black population growth over the last decade, all of them are in the suburbs of these metro areas.

And that could play right into the hands of a Republican Party that controls redistricting in an unprecedented number of states and will be drawing many of these districts.

“The practical effect is great for the GOP; in state after state, it’s allowing Republicans to pack more heavily Democratic close-in suburbs into urban black districts to make surrounding districts more Republican,” said Dave Wasserman of the Cook Political Report.

In effect, the Voting Rights Act makes it permissible for Republicans to combine as many black voters – the most reliable Democratic voting bloc in the country – into some of the most creatively drawn districts in the country. This is known as “packing,” and while it makes for a series of very safe Democratic districts, it also takes Democratic voters out of neighboring districts — making them easier for Republicans to win. (“Packing” is a form of gerrymandering — the process of benefitting politically by drawing districts that are often oddly shaped.)

The migration is staggering in many areas.

Detroit Democratic Reps. John Conyers and Hansen Clarke, for instance, lost nearly one-quarter of the 800,000 black voters their districts had in 2000. But Rep. Sander Levin’s (D) neighboring suburban district took in many of those voters, gaining the ninth-most black voters in the country. Nearby Reps. Thad McCotter (R-Mich.) and Gary Peters (D-Mich.) also saw their district pick up tens of thousands of African-Americans.

Ditto Washington, D.C., which saw its black population plummet 11 percent over the last decade, while suburban D.C. Rep. Steny Hoyer (D-Md.) gained more black voters than anyone outside of the fast-growing Atlanta area. (Fellow Maryland Democrats Donna Edwards and Chris Van Hollen also gained lots of black voters.)

The effect of all this movement is that the black population is significantly more dispersed than it was a decade ago — even as the Voting Rights Act continues to require black-majority districts not be diluted during the redistricting process.

In other words, significant line changes will have to be made to keep these districts as heavily black as they were for the last decade.

The most extreme case is in Louisiana, which became the first state to complete its congressional map this month.

Outmigration from Hurricane Katrina dispersed black voters from New Orleans all over Louisiana (and also into Texas and Mississippi). So while Rep. Cedric Richmond’s (D-La.) New Orleans district lost more black voters than any other district in the country – nearly 120,000 – all the states’ others districts gained black voters. That meant his district needed to be stretched to Baton Rouge in order to pick up black voters and keep a semblance of its old black majority.

Of course, in the process, the five Republican-held seats in Louisiana got very safe for the GOP. A vote analysis from the liberal-leaning Swing State Project shows Richmond’s district would have gone 73 percent for President Obama, while Obama wouldn’t top 40 percent in any of the state’s other five districts.

And that reality exposes the potential political peril for Democrats in the Voting Rights Act.

While hailed as an advance in civil rights that has helped many African-American politicians get to Congress, many experts and political observers acknowledge the long-term effects of the VRA have been good for Republicans, not Democrats.

Given the population losses in many of the country’s majority-black districts, and the fact that Republicans control redistricting in so many states, we can wager a guess that these majority-black districts will remain intact and possibly even add black population.

And the more gerrymandering, the better for Republicans.

The expanding of Clarke’s and Conyers’ districts, for example, could help Michigan Republicans eliminate a Democratic district in the Detroit area (possibly Peters’). The same goes in Ohio, where Rep. Marcia Fudge’s (D) loss of 29,000 black voters means her district will have to grow and Republicans can more easily collapse some nearby Democratic districts.

There is also room for the GOP to create some new black-majority districts – something they may very well try to do. If they make Rep. Sanford Bishop’s (D-Ga.) district majority-black, it could help keep freshman Rep. Austin Scott (R-Ga.) safe by taking Democrats out of his neighboring district. And Republicans could push Philadelphia Rep. Bob Brady (D-Pa.), a white Democrat, into a majority black seat, a move that might help them shore up all the suburban seats they hold nearby. (Both Brady’s and Bishop’s current districts were over 48 percent black in the Census.)

Hilary Shelton, the Washington bureau director for the National Association for the Advancement of Colored People (NAACP), said his organization is prepared to fight the over-packing of majority-black districts and hopes that Republicans won’t overplay their hand.

“On one hand, we like to see cohesiveness of those who share common values,” Shelton said. “But it is important that we don’t end up with the kind of packing in districts that actually” diminishes the influence of black voters.

The NAACP fought Texas’s mid-cycle redistricting plan very much on these grounds, and observers say there is growing evidence that black districts with super-majorities over-concentrate the black vote.

Some even contend that the Voting Rights Act has outlived its usefulness in this regard, as black politicians have made gains and regularly get elected even in majority-white districts. A pair of black Republicans even won in 2010.

But while the African-American population has been shrinking in many of these majority-black districts in recent years, the number of majority-black districts has actually increased over the last decade and could very well continue to with Republicans leading the redistricting process.

But while the expansion of these majority-black districts in 2010 might be a good thing in the short-term for the GOP, the minority populations are still growing much faster than the white population — especially Hispanics. And given the GOP’s struggles with minority voters, they may very well have a long-term problem.

“Without question, the last election came at a perfect time for Republicans in terms of taking control of a lot of state legislatures that they hadn’t before,” said David Bositis, an expert on race and politics at the Joint Center for Political and Economic Studies. “But the underlying fact is that, if you look at population growth of the U.S. over last 10 years, almost all of the growth came in minority communities.”

In the meantime, there could very well be battles over just how many black voters must be put in these majority-black districts.

And with a Democratic-led Justice Department for the first time since the Voting Rights Act passed, those battles could be more pitched than they have been in the past.