Wait But Why sums up the nation’s history through Lincoln in one sentence:

Aggressive (and controversial) expansion of United States territory exacerbated the nation’s tensest and most divisive debate—slavery—by forcing the question of whether the new territories should be able to self-determine whether or not to allow slavery, highlighting the haziness around where state rights end and federal power begins and accelerating the nation toward Civil War.

Here is a fascinating blog entry with lots of neat statistics and facts about the American presidents and history.