In a word, taxes. That and import/export policy. The south was rural and agricultural, the north was much more industrial, even in 1860. Thus policies that favored industry over agriculture hurt the South and forced it to change it's ways.
The main reason the south lost was because they were not as industrialized as the north, and because they had a much smaller population, in part because of all the immigrants, many of whom were employed in that industry. The plains states were not much of a factor, as they were barely beginning to be settled at that time, and were still considered to be part of the Great American Desert, not suitable for agriculture. In part because of the drought cycle which was at it's peak when the area was first explored, and in part because people thought grasslands had less rich soil than forests. (In reality the opposite is true, but it's especially not the case when the grassland is the American Great Plains, a legacy of the last ice age).
I think that is somewhat of an oversimplification. Kansas, Nebraska, Iowa etc were agricultural and thrived after the war. I still don't understand what "ways" the culture was changed. No one has yet explained in any clear fashion what was the culture of the south that made it unique? The idea of a southern culture, which I am sure existed, is wrapped in so many myths it is hard to seperate the real from the false. I honestly believe whatever culture was unique after the civil war has for the most part been watered down by outside influences and only exists in the minds of a few diehard Southerners.