Following its inception in the late 1790s, the Democratic Party, originally called the Democratic-Republican Party, worked for the political aims of the slaveowners of the South. The founder, Thomas Jefferson, owned slaves. As the sin of slavery became more and more apparent to Americans, the Democratic Party began to suffer internal strains. Indeed, in the pivotal 1860 election, the Democratic Party split into two factions and each faction had its own candidate. The reason why was because the Democratic Party couldn't remain loyal to both its allies in the Southern ruling class and get the votes of Americans who wanted to abolish slavery.
From 1860 to 1876, the Democratic Party was out of power in Washington. The Southern ruling class, which had lost the Civil War, wasn't able to control the Reconstruction governments of the states of the Old Confederacy. That all began to change, however, following the disputed election of 1876.
In that election, Democratic candidate Samuel Tilling, governor of New York, almost defeated the Republican candidate, Rutherford Hayes. The election was thrown into the House of Representatives. Hayes managed to pull out a win, but the price was that he agreed to withdraw United States troops from the South. He ended Reconstruction.
The ending of Reconstruction meant that the white majority of the Southern states could grab control of the state governments, which they did, and it also meant that they could establish segregation, which they did. The refusal of the United States Supreme Court to rule segregation unconstitutional in the Plessy case meant that black Americans had no way to force the state governments of the South to recognize their civil rights.
From 1876 to 1948, the Democratic Party did not challenge this state of affairs. That ended in 1948 when the young Mayor of Minneapolis challenged the status quo and forced the Democratic Party to adopt a civil rights plank. Strom Thurmond and the so-called Dixiecrats walked out, formed their own party, appeared on five Southern ballots in 1948, and the so-called "Solid South" began to crack.
The cracking was patched over in the 1960 election, with electoral slates loyal to John F. Kennedy carrying most southern states. The passage of the 1964 Civil Rights Act, followed by the Voting Rights Act, drove Southern whites out of the Democratic Party. By 1972, Nixon was following the Southern Strategy and Democrats lost every state in the South. (Of course, McGovern lost all states but one, but the writing was on the wall for Democrats in the South.)
Jimmy Carter managed to get back some of those southern states in 1976, cut lost them to Reagan in 1980. Mondale lost them in 1984 and Dukasis lost them in 1988. Clinton, though, was competitive in the South in both 1992 and 1996. Gore, however, in 2000, was not, and neither was Kerry in 2004.
In politics, though, as in life in general, nothing lasts forever. Obama actually took three southern states, Virginia, North Carolina, and Florida, on his way to winning the presidency. Not only did he take three southern states, but he proved that a candidate who was not a white southerner could win the presidency.
In a way, the election of the first African-American President as a Democrat represents an atonement of sorts for the Democratic Party's racist past. It doesn't excuse it, it doesn't make it disappear, and it doesn't repay all those African-Americans whose rights were denied for decades in the South, and indeed, in the United States. But, it is an atonement of sorts. As a Democrat, I am proud and glad that my party was the first major party to nominate an African-American for president. As an American, I am even prouder of my country for electing him.