In June 1776, just a month before the Declaration of Independence was ratified, the white men of Barnstable, Mass., voted on whether America should break its bonds with Great Britain. The tally: 30 for independence, 35 against and 65 abstentions. These days, the Colonists who opposed the revolution have been all but forgotten. Yet, in the years leading up to the Revolutionary War, as many as a fifth of those living in America wanted to remain British subjects. Probably at least that many again were apathetic or opportunistically waiting to see which side won. The American Revolution, many historians argue,...