Oh boy, a question I’m qualified to answer!

The Democratic Party has a history of being a “big tent party.” You may have heard that phrase before. Well, the party came into it’s modern form under Andrew Jackson and was largely centered around agrarian populations in the South. Living in the south and on farms led the Democrats of the time to be pro-slave and socially/fiscally conservative.

The Civil war came about and most of the Democratic states (the South) break away. The South loses and the Reconstruction begins. Slaves for a brief while get the right to vote. This leads to massive backlash to Democratic politicians. Southern Republicans and Republicans from the North (carpetbaggers) come in and start making in-roads. However, Andrew Johnson effectively ends the reconstruction and soon Democrat’s start gaining power again. The Ku Klux Klan is founded and Jim Crow laws start to be instituted. Southern Democrats were almost entirely centered upon the oppression of minorities, especially former slaves.

Skip to the early 1900s, and the Progressive Era begins. By 1904, the political divide* is still very much North vs South with the GOP in the North and West and the Dems in the South.

However, Progressive labor laws, women’s suffrage and such get launched into the forefront of politics around this time, as well. The Progressive Party is formed, nominates former President Teddy Roosevelt, and splits the vote with the GOP, leading to a massive Democratic landslide throughout the country. Dem nominee Woodrow Wilson wins with 435 electoral votes in the 1912 election.

In 1916, the Progressives and Republicans try to unify, but Teddy Roosevelt denies the nomination and the Progressive Party crumbles. Teddy suggests those voters go support GOP politician Charles Evans Hughes, and some do, but many go on to join the Democrats, such as Harold Ickes, who did a lot of the work for the New Deal under FDR. Ickes was different than other Democrats, he was a northerner and also the President of the Chicago NAACP. Progressive policies get spread to each major party, but for the Democrats, it’s mostly in the North.

This leads to a situation where Northern Democrats and Southern Democrats are in the same party, but ideologically opposed in many ways, as you have noticed. Over the next decades, the Democratic Party uses this to their advantage. The GOP under Hoover adopts a hands off economic approach, the Great Depression happens and Hoover is blamed. The Democratic Party adopts a more hands on approach under FDR with the New Deal. FDR, a northerner, navigates the North/South divide very well, and it leads to Democrats dominating American politics for decades after.

The tensions get worse between the factions eventually, but the Solid South is still very Democratic. In 1960, there’s a fracture in the South where Mississippi and Alabama vote for a Southern Democrat from Virginia, Harry Byrd, instead of Northerner Democrat, JFK. The South is still on the Democrats’ side, though. That changes with the Civil Rights protests in the 60s. When Lyndon Johnson signs the Civil Rights Act of 1964, the South breaks away from the Democratic Party almost immediately. Republican Barry Goldwater runs against LBJ on a platform against the civil rights act and pro-states rights. Five Southern states (Louisiana, Mississippi, Alabama, Georgia and South Carolina) break away and vote republican.

In 1968, when Hubert Humphrey ran against Nixon, the only state to vote Democrat in the South was Texas. The Southern Democrats formed the American Independent Party on a pro-segregation platform and carried the South in 1968, but Nixon ended up winning. In 1972, under the Southern Strategy, Nixon adopted* much of the American Independence Party’s platform and subsequently swept the South. He also won just about every other state too (520 electoral votes) but he was the first Republican to win the South. After Watergate, Carter, a Southern Democrat, wins the South in 1976, but he was much more like a Northern Democrat than a Southern one. In 1980, Reagan sweeps the South running with a mix of Nixon and Barry Goldwater’s campaign strategy. He doesn’t pick up Georgia, Carter’s home state, though. He wins it in 1984, however.

The South votes for the GOP candidate almost exclusively from then on. Bill Clinton does well in some southern states, but he was also a moderate Southern Democrat.

*edit: words