During a Biblical seven years in the middle of the nineteenth century, fully a quarter of Ireland's citizens either perished from starvation or emigrated in what came to be known as Gorta Mor, the Great Hunger. Waves of hungry peasants fled across the Atlantic to the United States, with so many dying en route that it was said, "you could walk dry shod to America on their bodies." In this sweeping history Ireland's best-known historian, Tim Pat Coogan,...