But if slaves were so valuable, there would have been breeding farms which raised only food for the 'livestock' and slaves (didn't happen). If slaves were so valuable, do the descendants of these slave owners not have a case against the North for siezing their property and denying them the use and ownership of that property. Kinda changes the Reparations picture, doesn't it?
Opening new territory without the ability to farm it was useless to both the North and the South. If the Southern economy depended on slaves, then the Northern economy depended on slaves, too, or the raw materials base the North exploited would vanish. Similarly, the Tarrif revenue would vanish as fewer goods would be imported when Southern production came to a standstill. My data is from Maryland, where tobacco harvests were increasingly able to be handled by larger families. And, due to the seasonal demand for labor, slavery was becoming less economical. (Yes, Virginia, Maryland was a Southern State, but y'all took too long to vote on secession, and by then Maryland had been occupied by troops from up north.)
Slavery did not become an defining issue until the North needed Cannon fodder (black troops) and the North tried to foment a rebellion of slaves in the South against their owners, in 1863.
Actually it did. Virginia and North Carolina were two states which had very active industries of raising and selling slaves to the rest of the southern states, where demand far outstripped supply. In fact, the confederate leaders recognized the importance of this supply when they specifically protected imports of slaves from the slave-holding states of the U.S. in their constitution.