"The attempt by eleven southern—and slaveholding—states to secede from the Union in the winter and spring of 1860-61 presented the United States with the greatest internal political challenge it had ever faced. Because the Constitution had created a federal Union, secession (which broke the ties of Union) was a dagger at the heart of the American polity. The fact that this secession was motivated by Southerners' determination to protect their investment in human slavery added a cruel twist of the blade. Not only did secession fracture the Union, it did so on behalf of a practice which obliterated the fundamental natural right to liberty, which the federal Constitution was supposed to protect."