The Civil War was not about slavery, but was about the SPREAD of slavery. Lincoln was fine with slave states retaining slavery. He was absolutely opposed to the spread of slavery to new states or territories. But this ran afoul of the interests of wealthy planters who, both wanting and needing more land, were determined to move their slaves ever westward.Cotton apparently depletes the soil more than many other crops. So planters needed new fields in which to plant/harvest cotton. Thus, there was something of a need for new land in which to grow cotton (and, subsequently, the need for, as they saw it, slaves to make it happen).However, much of it was greed. Those who grew wealthy wanted more wealth. And those without wealth wanted more wealth, too. And in the southern mind, cotton was king. Why plant cotton in this field this year, but in that field next year? Why not plant in BOTH of them?