As James Naughtie concludes his series about the ideas tying America's birth 250 years ago to the United States today, he examines freedom, asking whose freedom, and what kind?

He begins in Gettysburg, attending a re-enactment on the battlefield made famous by an address from President Abraham Lincoln in which he asked whether the United States "could long endure". That question is being asked again now, as Americans experience profound disagreements over many of the ideas in this series - economic opportunity, justice, freedom; even what it means to be an American. As he hears, American history itself has become a battlefield. And so speaking to historians with different perspectives, and senior political leaders from both parties, James assesses how dangerous this moment is for United States.

Producer: Giles Edwards