Fueled mainly by the issue of slavery, the question came up during the 1820s and the 1830s, 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, both had adopted extreme positions, which were based on the morality of slavery and economic self-interests. As long as both North and South had equal representation in the US Senate, neither side could dictate to the other. However, with each new state applying for statehood, the balance of power was threatened. In the 1850s, the issue of secession was raised again. The South made the argument was that when it agreed to join the United States in the late 1780s, it 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.”