During the founding period alone (not Civil War era), was there any arguments at all from thinkers during that time positing that there just be two countries? It seems like many thinkers (Jefferson, Madison, and many more) saw the ruinous nature of slavery and it was fairly obvious that this would be a HUGE problem down the road. Even during their own period, there was significant compromises to keep the nation together.
However, it seems kinda odd that they have such a huge commitment to keeping the entire country together rather than just having a group of Northern states who abolished slavery and an unrelated group of Southern states who can go their own way. I understand they fought the Revolutionary War together, but it still seems very early on into a nation to have a national identity that one would sacrifice huge ethical principals to keep the country together.
Maybe I'm mistaken or the answer is obvious though... Were there other, more practical reasons? Was the Northern economy entirely contingent on the Southern states being around? Someone just enlighten me here.
edit: just to be clear, my main question is if any thinker of this time mentioned this AT ALL. Secondary is wondering why this didn't happen
No, and for a few reasons. First, slavery was not only a Southern institution: every colony permitted slavery at the start of the war, and most still allowed for it at war's end - though of course slavery was far more important to the economic and social functioning of the Southern states. Secondly, many of the Founders, particularly Jefferson and his ilk, considered their state governments more important to their daily lives than the federal government. These men considered an immediate federal intervention to end slavery extremely unlikely, to say the least. This was due, in no small part, to the fact that property rights - and thus slavery - were well-defended in the Constitution and Bill of Rights.
There is also evidence to believe that a fair number of the Founders did believe that slavery could die a natural death. The Constitution stipulated an end to the Atlantic slave trade (though this may have had less to do with humanitarian interest than with increasing the sale price of slaves for those that already had slaves to sell), and the Confederation Congress passed the Northwest Ordinance that banned slavery from the territory north of the Ohio River.
Slavery did not become THE great wedge issue in national politics until the late 1840s, when sugar cotton monoculture and the annexation of Mexico removed Congress' ability to defer the slavery question any further.
Sources:
David Blight, Race and Reunion
Allen Guelzo, Fateful Lightning
James McPherson, Battle Cry of Freedom
Gordon S. Wood, Empire of Liberty
David Waldstreicher, Slavery's Constitution