Moreover, the Republican party wasn’t even formed until the 1850s. The party was formed as an anti-expansion-of-slavery-states party.
Whigs or democrats ran the country and both parties owned slaves.
That's what they publicly claimed, but the truth that was unknown to the public at the time, was that slavery could not expand outside of the states where it already existed. The issue of "expansion" was a false issue. It was just propaganda.
I now see the Republicans as a "let's keep control of the government" party that used slavery as an excuse just to gain and hold power.
Why? Because they and their cronies were getting rich from controlling the government by taxing the Southern states at 72%, and forcing them to hire their companies for services (such as shipping cotton) and using government power to force the South to buy their products.
The government had been rigged to pull money from the South and put it into the pockets of wealthy well connected rich liberals in the Northeast. (In those days, the Republicans were the liberals.)