This story is tucked inside Adam Gopnik’s great survey of John Stuart Mill’s thought:

[Mill] helped to save the American Union. Few Americans learn that the cotton spinners of Lancashire were among the heroes of the Civil War. Out of work and starving, because of the Union blockade of cotton imports from the Confederacy, the workers nevertheless supported the Union out of pure anti-slavery principles. Had England recognized the South, and acted to end the blockade, as nearly happened several times, the Union would have lost, no matter what Grant or Lincoln did. It didn’t happen, because the Lancashire workers were so against it; when the great American historian John Jay Chapman listed the English liberals whose words were most responsible for the workers’ resistance to slavery, he placed first the name of John Stuart Mill.