The northern states invested large amounts in infrastructure and education, the southern states didn't. Unfortunately, the ideology that the rural life/slavery society had spawned and that rejects government infrastructure and education investments persisted through the civil war and right up to the present day, and so the vast majority of the south never caught up.
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Well now they actually didn't reject it. Those who remained along with the powers at be up North and others such as the Lehman Bros. who moved up there, were behind builing infrastructure that got the raw resources to their markets, but not the local communities markets.

German cowboys from feudal families in Europe, not German immigrants to here, in the west had to hire Texans because they didn't know diddly about what they were doing, but it kept the little spoiled rich boys busy.