The Republicans favored national, rather than state, bank charters. I suppose that counts as centralization, but nowhere near on the 20th century scale. Seen in the context of the 19th century they were the national or centralizing party, but there was a big difference between what they intended and what, say, Lyndon Johnson, Teddy Kennedy or Walter Mondale wanted. The Democrats were the localist, state's rights party, but when one looks at what "state's rights" involved after Reconstruction, one can understand why lovers of liberty might still prefer the Republicans. Along the same lines, some will attack the Republicans for creating an empire, rather than a republic, but this ignores the expansionism of antebellum Democrats. Before the war, opponents of empire might well have been Whigs or Republicans.
Where the Confederacy fits in is another question. Their history ended in 1865. Had the Confederacy lasted, it would surely have had its own centralists and imperialists.
If the Dems of that day were so in favor of States Rights, why did they push through legislation like the Fugitive Slave Act which trampled not only states rights, but individual rights? Why did they favor Dred Scott which for the first time in history told states who could and couldn't be a citizen of a state and effectively nullified equal protection under state constitutions?
The Slave Power (Democrat Party) didn't give a damn about states rights.