Massachusetts abolished enslavement before the Treaty of Paris brought an end to the American Revolution, in 1783. The state constitution, adopted in 1780 and drafted by John Adams, follows the Declaration of Independence in proclaiming that all “men are born free and equal.” In this statement Adams followed not only the Declaration but also a 1764 pamphlet by the Boston lawyer James Otis, who theorized about and popularized the familiar idea of “no taxation without representation” and also unequivocally asserted human equality. “The Colonists,” he wrote, “are by the law of nature free born, as indeed all men are, white...