The play takes place in and around New Salem, Illinois, in the 1830s, then in Springfield, Illinois, in the 1840s, and in Act III in Springfield in 1858 to 1861. It is based principally on the 1926 biography Abraham Lincoln: The Prairie Years by Carl Sandburg, which covers Lincoln's life up to his inauguration as President. The play depicts Lincoln's evolution from unambitious backwoodsman to a champion of freedom, and relies on the audience's knowledge of Lincoln's subsequent career to color the portrayal of his character. Sherwood wrote the play as a riposte to isolationist sentiment in the United States in the lead-up to the Second World War; he had fought in the First World War but had been disappointed by the way the post-war world had turned out. The play emphasizes the need to overcome laissez-faire sentiment and to stand up and take firm political action for the public good. As its star Raymond Massey put it, "If you substitute the word dictatorship for the word slavery throughout Sherwood's script, it becomes electric with meaning for our time."
