When California's new redistricting commission was divvying up the state's 38 million residents among 177 legislative, congressional and Board of Equalization districts in 2011, the federal Voting Rights Act loomed large.

Why it did requires a bit of historical background.

The 1965 Voting Rights Act was aimed at correcting the systematic exclusion of blacks from voting in Southern states. It used a formula, having to do with racial and ethnic populations and voting patterns, to identify states and localities whose electoral practices would be overseen by the U.S. Justice Department.

Four California counties — Kings, Merced, Monterey and Yuba — fell into the category due to the formula.

Why? All four were and are rural with relatively small populations, and relatively large nonwhite — mostly Latino — populations. But the decisive factor was that all had large military installations.

Most of the personnel at Lemoore Naval Air Station, Castle Air Force Base, Fort Ord and Beale Air Force Base were really residents of other states, but the census counted them as residents of those four counties. Therefore they figured into — and skewed — the Voting Rights Act formula.

Nonsensical? Yes, but once a locality went on the Voting Rights Act list, removal was very difficult, bordering on impossible. Although Fort Ord and Castle AFB closed almost two decades ago, it wasn't until last year, after a costly legal battle, that Merced County finally escaped federal oversight.

The Voting Rights Act has not only affected local matters — even the placement of voting booths — but the decennial redrawing of legislative and congressional districts for the whole state.

After the 2000 census, for example, the Capitol's dominant Democrats made a status quo deal with Republicans, in part because they feared that the Bush administration's Justice Department could have rejected a Democratic gerrymander.

The redistricting commission, which took over the task after the 2010 census, assumed that because of the Voting Rights Act, it had to maximize chances for Latinos and other specified population groups to elect legislative and congressional representatives — not only in the four counties but throughout the state. That assumption had the effect, intended or otherwise, of increasing Democratic numbers.

The Voting Rights Act's dominance on redistricting, however, may have come to an end. On Tuesday, the U.S. Supreme Court, by a 5-4 vote, ruled that the static 1965 formula cannot be applied 48 years later and that Congress should devise a new one.

The old formula is out, and any new one — if Congress acts — is likely to exclude California. Ironically, the decision comes at the precise moment that Latinos are becoming the state's largest ethnic group and will be claiming an increasing share of political power.

Dan Walters is a columnist for the Sacramento Bee.