Sean Wilentz is professor of history of Princeton University and a former fellow at the Woodrow Wilson Center.

Something extremely important happened in American society between 1812 and 1861. Just as the country accelerated its westward expansion and adjusted to the industrial revolution, it progressively redefined its understanding of democracy. From that time to this, inclusiveness has been a central issue in the American political system. As different groups state their claim to the promise of democracy, the conception of what democracy is all about is expanded. Sean Wilentz describes how this has worked.