The Civil War, as we have seen, grew out of major differences dividing the North and the South. Slavery stood at the heart of these differences, yet the North went to war claiming that its sole purpose was to preserve the Union, and the Confederacy insisted that it was fighting for independence, not slavery. The ideals and arguments of both sides drew upon the American past. Supporters of the Union denied, as Jackson had denied in his proclamation on nullification, that any right of secession existed under the Constitution. As in the nullification crisis, supporters of the Union linked the survival of democracy with the Union's preservation, and they upheld the idea of America's mission going back to the Revolution and ultimately to the founding of the Puritan settlement of the Massachusetts Bay colony. Confederates argued, as had Calhoun in the nullification crisis, that a state had the right to secede under the Constitution. In establishing the Confederacy, southerners declared that they were acting on the principle of self-government, as proclaimed by the Revolution's leaders in resisting tyranny in 1776. Both the North and the South sought to preserve the situation as it existed before the disruption of the Union, but the war unleashed forces that required both sides to adopt new ideas and principles. In the process, the meaning of the Civil War became fundamentally transformed.