The novelist Harriet Beecher Stowe, born 200 years ago today, was an unlikely fomenter of wars. Diminutive and dreamy-eyed, she was a harried housewife with six children, who suffered from various obscure illnesses worsened by her persistent hypochondria. And yet, driven by a passionate hatred of slavery, she found time to write “Uncle Tom’s Cabin,” which became the most influential novel in American history and a catalyst for radical change both at home and abroad. Today, of course, the book has a decidedly different reputation, thanks to the popular image of its titular character, Uncle Tom — whose name has...