A horrifying epidemic of smallpox was sweeping across North America when the War of Independence began. This work reveals how deeply this disease affected the outcome of the war in every colony and the lives of everyone on the continent. It shows how the disease devastated the American troops at Quebec and kept them at bay during the British occupation of Boston, and how it ravaged slaves in Virginia who had escaped to join the British forces. During the terrible winter at Valley Forge, General Washington had to decide if and when to attempt the risky inoculation of his troops. The destructive, desolating power made for a cascade of public health crises and heartbreaking human drama. This work shows how this tragedy was met and what its consequences were for the young republic.