Slavery’s western expansion created problems for the United States from the very start. Battles emerged over the westward expansion of slavery and over the role of the federal government in protecting the interests of slaveholders. Northern workers felt that slavery suppressed wages and stole land that could have been used by poor white Americans to achieve economic independence. Southerners feared that without slavery’s expansion, the abolitionist faction would come to dominate national politics and an increasingly dense population of slaves would lead to bloody insurrection and race war. Constant resistance from enslaved men and women required a strong pro-slavery government to maintain order. As the North gradually abolished human bondage, enslaved men and women headed north on an underground railroad of hideaways and safe houses. Northerners and southerners came to disagree sharply on the role of the federal government in capturing and returning these freedom seekers. While northerners appealed to their states’ rights to refuse capturing runaway slaves, white southerners demanded a national commitment to slavery. Enslaved laborers meanwhile remained vitally important to the nation’s economy, fueling not only the southern plantation economy but also providing raw materials for the industrial North. Differences over the fate of slavery remained at the heart of American politics, especially as the United States expanded. After decades of conflict, Americans north and south began to fear that the opposite section of the country had seized control of the government. By November 1860, an opponent of slavery’s expansion arose from within the Republican Party. During the secession crisis that followed, fears nearly a century in the making at last devolved into bloody war.