"But starting in the seventeenth century and continuing through the nineteenth century, slavery came under attack. The attack was two-pronged. The first prong of the attack was the American founding, which had no power to end slavery but which established a framework for reducing, corralling, and ultimately placing slavery on a path to extinction. The second force, which emerged almost a century later, was the Republican Party, a party explicitly founded to block and then eliminate slavery, healing the "crisis of the house divided" and creating a single union of free citizens."