Most black voters are women - about 64 to 66 percent according to most estimates. Black women in the 2000 election voted about 95 or 96 percent Democrat (of the few black Republicans, a majority are men). When you take this into account, you realize that white women are almost evenly divided between Democrats and Republicans. Married white women are more Republican than Democrat.
During the Clinton years, of all single and divorced women, the Democrat-Republican split was about 70-30. This figure includes black women, who are not only disproportionately Democrat but also disproportionately single. Although black Americans are about 12 or 13 percent of the population, black women may make up as much as 20 percent of the single/divorced female electorate. Blacks are the loneliest Americans in domestic terms; about 40 percent of them never marry.
Some posters have discussed the decline of marriage, an issue I take seriously and follow closely. This isn't the time for a long exposition, so may I just say that there are some indications that this bad situation is no longer getting worse, and marriage may even be making something of a comeback. There is some interesting stuff on Mickey Kaus's site kausfiles.com that you might want to read. It describes some indications that the number of children living with their two biological parents has risen slightly, perhaps partly as an effect of welfare reform.