The headline out of Alabama lays it out:

The court pointed to voter registration numbers from 1965
and 2004 in the six original states, including Alabama, that Congress had when
it reauthorized the act in 2006. In Alabama, for instance, whites were
registered at 69.2 percent while African-Americans were at 19.3 percent,
showing a nearly 50 percent gap. By 2004, the levels were almost even with
whites at 73.8 percent and African-Americans at 72.9 percent.