Slavery affect the economy, social, and class system in the South due to the agriculture economy. Slavery formed the backbone of their economy. The slaves help them cultivate their crops, while the owner just keep the money. Then after the invention of the cotton gin, slavery became the nub of the their political and social basis.
Slavery in the north had very little affect in the northern's economy, social, and class system. It is because slavery in the north is less integral to the economy. Even though slavery was integral in the north, the northern industry and commercial are interested in the sustainability of slavery in the South. The northern textiles industry relying on the south became more intense due to the invention of the cotton gin.
During the 1850s, the United States finally gain control over the west territories. The government did not want to tolerate slavery in the west. But there was great controversies between the south and the north so to just please the south a little bit. The slave owners all wanted slavery to be everywhere, because of the Missouri Compromise. This debate was going on for a long period of time.