Nope. There were at least six different parties that combined into the Republican party. The largest was the Order of the Star Spangled Banner - a.k.a. the Know Nothings. (They were the largest mainly because they overlap with all of the other parties.) The second largest was the Whig party. The third largest was the Anti-Mason party, Then came the Free Soilers, the Liberty Party, and a few others.
The Free Soilers were certainly the most perfidious. They had a history of stabbing their coalition partners in the back. For instance, they betrayed the Whigs and joined with the Democrats in Ohio and Massachusetts to give the Democrats control of those legislatures. In exchange, they got to name one US Senator from each state. That's how we wound up with two of the most vile creatures ever to sit in the US Senate: Charles Sumner and Salmon Chase. When the Republican party was formed both men turned their coats again and joined the Republicans.
It was primarily a 'mid-western' party opposed to the expansion of slavery negros to the territories - There. Fixed it.
The Free Soilers are the ones who funded John Brown's terrorist activities. When Brown killed those people in Kansas and kidnapped their bondsmen, he did not set the slaves free. He took them to the Canadian border and deported them. Harriet Beecher Stowe was also a looney Free Soiler and you may recall the negro subjects of her novel deported themselves at the end of the story. The slavery issue was always really a Negro issue. Indiana, Ohio, and Illinois amended their state constitutions banning the entrance of any negros, free or slave. They opposed slavery because slavery meant negros.
Once the Republican party got itself organized the former Whigs, who had the most experience in politics, quickly came to dominate it. The Whigs stabbed every other party that had joined the Republicans in the back, abandoning every agenda except their own. They abandoned the anti-immigrant/anti-Catholic stance of the Know-Nothings. Thadeus Steven's whole crazy anti-Mason thing disappeared and was never spoken of again. They abandoned the anti-slavery position of the Free Soil and Liberty parties. Remember Lincoln threatened the northern states over enforcement of the Fugitive Slave Act in his inaugural address. Then there was the Corwin Amendment, the I-would-also-do-that speech, etc. The one and only agenda the Republicans stayed true to was the Henry Clay American System of high tariffs, central banking, and corporate welfare. It's what the party was about. It's what the war was about. It's what they proceeded to implement the minute they got in power.
In the 'Deep South' in the 1850s, it would have been suicidal, literally, for any politician or his supporters of any party to oppose slavery or the expansion of slavery in any way. It would have been like a Jew looking to run for office in Iran today. They would have been killed.
That's a bit of a strawman isn't it? Lincoln campaigned against abolitionism in 1860. And you keep equivocating between anti-slavery and anti-expansion as if they are the same thing. Anti-expansionism is about excluding negros, free or slave. How could it be that slavery is just in the South, but unjust in Kansas? The anti-expansionists wanted to exclude all negros.
Why not take the Republicans at their word.
No man has the right to be surprised at this state of things. It is just what we abolitionists and disunionists have attempted to bring about. There is merit in the Republican party. It is the first sectional party ever organized in this country. It does not know it's own face, but calls itself national; but it is not national - it is sectional. The Republican party is a party of the North pledged against the South. ...Wendell PhillipsWendell Phillips publicly declared his party to be "a party of the North pledged against the South", and you won't find any of his contemporaries contradicting him about it. This is why the Union broke up. Slavery, the tariff, and the disposition of the western territories all became super critical because the country suddenly had one entire section, the South, disenfranchised by and politically subordinate to the other (albeit through an election). There wasn't going to be any process of compromise anymore. After the election of 1860 the North would be able to simply impose it's own agenda on the South. That's why the South seceded.
The union didn’t break up. Rather, the slave power pretended authority for states that the states didn’t have, and then started an insurrection.