When Benedict Arnold realized his plan to defect to the British had been exposed, the first thing he did was tell Peggy Shippen, his loyalist-leaning wife who had helped him plan his treachery. After the war, Parliament announced plans to resettle refugees like the Arnolds in Canada in order to strengthen Britain’s power in its remaining possessions. Sixty thousand loyalists seized this opportunity—Shippen and Arnold among them. Yet the new lives that awaited the Arnolds there proved to be hard-scrabble, scarring, and wretched, a microcosm of the hardships faced by...