What did the Republican Party support that many southerners were opposed to?

When the Republican party was formed 1n 1854, its main plank was to keep slavery from expanding into the Western territories. Most of the landowners interested in settling these territories (especially Texas) were slave-holding Southerners. The Democratic party had been associated with Southern slaveholder interests since its inception, and Southerners associated the Republicans with Northern crusaders and busybodies.

Around the early 20th Century, the roles of the two parties began to shift. Republicans, who had been progressives up through the Theodore Roosevelt presidency, became more associated with big business. Democrats were morphing into two nearly separate parties, with Southern Democrats increasingly taking their own path.

By the Franklin Roosevelt administration in 1933, mainstream Democrats had become the liberal party (Black voters, loyal Republicans since Lincoln, were mostly lured over to the Democrat side by FDR) and Republicans had been the conservative one for a couple of decades. By the 1960s, the South was overwhelmingly Republican (although it would still yield a surprising number of Democratic governors and presidents).