Susan Schulten found a fascinating timeline, created in 1880, of American political party history up to that point. She explains the above image:
Notice how much the chart resembles a a river. The metaphor is useful — the wider the river at any spot, the more “powerful” the party at that time. I’m particularly impressed by the representation of the turbulent 1850s, when the Whig Party disintegrated and the Republican Party was founded.
[O]ne of the things that stands out to me is that the idea of a government permanently divided between Republicans and Democrats was a pretty new concept at the time this was drawn up. Parties had come and gone, with the major ones usually only lasting a few decades. That the parties warring for power in 1876 would be the same ones (more or less) doing so in 2012 would likely have seemed pretty remarkable to political observers at the time.
Via Andrew Sullivan.