"Resignation," the second episode of season 4 of HBO's Boardwalk Empire, airs tonight at 9. As the series progresses, more and more American history will come to bear on the story. Rather than watch with an encyclopedia open on your lap, just prepare for the less-well-known events discussed with this, a guide to historical context for some of the things that will be mentioned in tonight's episode.

No need to feel stupid watching television.

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