Fueled mainly by the issue of slavery, the question of what rights belonged to the state and what belonged to the federal government came up during the 1820s and 1830s. This is when the United States was expanding westward. Southern states wanted the new territories to allow slavery. Northern states wanted the territory to be free of slavery. As the North's economy grew and the South's economy stalled, the two began moving farther apart on the issue. By the 1840s and 1850s, each had adopted extreme positions based on the morality of slavery and economic self-interests. As long as both North and South had equal representation in the United States Senate, neither side could dictate to the other. But with each new state applying for statehood, the balance of power was threatened. In the 1850s the issue of secession was raised again. The Southern argument was that when they agreed to join the United States in the late 1780s, they kept the power to cancel the agreement. South Carolina threatened to secede unless the Senate passed a constitutional amendment to give the South “the power she possessed of protecting herself before the equilibrium of the two sections was destroyed.”