The nation's political divisions are rooted in geographic divisions, a trend that is clearly revealed by the changing party control of seats in the House of Representatives. Two decades of House maps show how Democrats have become the party of metropolitan America, particularly in the Northeast and the West. By contrast, Republicans are dominant in the heartland and in less-populous places outside the big metros, particularly in the South and much of the Midwest.

The chart below shows that in almost every election, the party that gains seats does so in all regions of the country. But amid those changes, the nation's geographic divide has widened. While the Northeast and West in 2000 showed much different political profiles than the South, those differences are substantially wider today.

House maps over time show the changing contours of the parties' strength in different parts of the nation.