The North was still building infrastructure so they didn't have to depend on expensive imports, mainly from England and Germany. It wasn't easy for them to export such things to countries that were better at making them.

The South was a huge producer of agrarian products, cotton and rice in particular, which were in great demand in Europe. They could be sold at a very high profit, because they were all produced entirely by the labor of slaves.

The money this brought in was in turn spent on luxury goods from Europe. Even during the war, the demand for luxury goods in the South was so great Lee couldn't get war materials through the blockades. The blockade runners were all carrying highly profitable luxury goods. That changed when Lee outlawed importing luxury goods entirely under threat of severe punishment.

England was the manufacturing arm and supplier of arms and ships to Confederacy. England, while closely allied to the South, did not actually enter the war, because, as fate would have it, they had a surplus of cotton in their warehouses at the time. They figured they could wait it out.

Of course, it wasn't all good. The Union captured a ship load of heavy cannons addressed to the Confederacy. They immediately moved to place them in action, but instead sent them to the scrap yard - the quality was so poor they were afraid they'd explode and kill more Union soldiers than Confederates.

Everything changed in Europe when the Union Navy took New Orleans from the south, while the Confederacy was preparing their defenses to the north.

The Europeans suddenly realized they were betting on the wrong horse, and cut off the lines of credit. Then they started looking for other sources of cotton and rice.

After the war, cotton continued to be produced, but could no longer be sold at such high profit - laborers had to be paid. Production of the famous Carolina rice was so dependent on slave labor it ceased to be grown entirely. It was an Indian Patna type, which is now grown as plain "Long Grain Rice" in Louisiana and Texas.

So yes, it was all about the money. The Southern elite knew that without slaves their days of leisure, luxury and pink teas would be over - because their products would no longer be so profitable in Europe.

Of course, they knew they would win. They had nearly all the elite officers, a lot of fortresses and equipment and a willing army. They also knew, from their newspapers and magazines that they were the "Master Race" and the people in the North were a "Servant Race".

Unfortunately for them, the Union also knew the South was going to win, and changed the rules. Now it was "Total War", where every man woman and child was part of the war effort, with production and logistics trumping bravery on the battlefield.

So much for the Master Race.

. . then why did production of Carolina Rice end with the end of slavery?

Besides, once you got a few slaves they were self replicating, and the surplus could be sold off (you say for the amount of 20 white men's labor for a year for each one).

And, of course, there was the "Fancy Trade", selling young black women as sex slaves, at a nice price. Hard to give that up, no?

And, if slaves were so expensive, exactly how could they all be bought and released? Maybe Salvation Army bell ringers could raise the money?

In any case, the southern slave owners would see that was a very short term pay off, that would be as severe a long term destruction of their economy as emancipation was.

And besides, the South was raring for a fight. They expected the war to be very short, and to be victorious over the "Servent Race".

I question your economics.