The North and the South were very different during the antebellum period. To begin with, the Northern economy thrived on its industrialization and textiles, while the Southern economy thrived on cash crops like cotton. These cash crops were produced by slaves forced to work on southern plantations. Many white citizens of the North cared little about slavery, since that institution depended more on the South than the North. However, this changed with the development of the Southern Cotton Kingdom. This required more land, which encouraged Southerners to expand their plantations westward. This movement was called Western Expansion. The expansion attracted the attention of many Northerners because they did not want the South to convert territories won in the Mexican War into slave territories. This conflict polarized the nation and led to civil war. The Kansas-Nebraska Act and the Dred Scott Affair were major factors that helped polarize the nation, as these events pitted the North and South against each other due to their opposing ideas on slavery, which ultimately led to civil war. The act was one of the main factors that polarized the nation until the Civil War. The Kansas-Nebraska Act stated that popular sovereignty would be the deciding factor in determining whether the territory would be free or slave. This motivated many abolitionist and pro-slavery supporters from both the North and South to settle in the Western territories. This would ensure that the vote for slavery would be in their favor. Knowing this, Senator William Seward, an abolitionist, declared: "We will enter into a competition for the virgin soil of Kansas, and God will give victory to the side which is in the middle of the paper." I should be able to stay and become a free black. Not only did white citizens hate this, but free blacks were becoming afraid. Southerners illegally captured free blacks and brought them to the South for profit. Now that southern slave owners could bring their slaves to the North, there was no longer any way to tell the difference between a slave and a free black man. This would give Southerners an excuse to claim free blacks as slaves, since they could easily say that they brought the slaves to the North with them. This would obviously upset Northerners, as many of them were abolitionists who wanted to end slavery and therefore believed that capturing free people for profit was wrong. In summary, the Dred Scott case favored the South and its decision angered the North because it was seen as unconstitutional. For these reasons, polarization in America worsened and civil war broke out..