Marx and Engels wrote it in six weeks at the end of 1847, a pamphlet for the Communist League that became one of the most influential documents in human history. The opening is famous: a specter is haunting Europe. The closing is imperative: workers of the world, unite. Between them, a compressed analysis of capitalism, class struggle, and historical materialism that changed how millions understood the world. You may disagree with every word. You cannot understand the twentieth century without reading it.