Ever heard of National Brotherhood Week? If you Google it, you'll see a video of a man in a coat and tie sitting in front of a piano. It's Tom Lehrer, a math professor turned musician-satirist, mocking the idea of National Brotherhood Week in the 1960s. But National Brotherhood Week was celebrated for decades in the United States, particularly in the '30s, '40s and '50s. And historians say it had an impact on the way Americans think of themselves.