Contrary to previously-held views, this book argues that a unique late marriage pattern explains the continuing puzzle of why Western Europe was the site of changes that gave birth to the modern world. It contends that the roots of modern developments are located in history more than a millennium earlier, when the peasants in northwestern Europe began to marry their daughters almost as late as their sons. This phenomenon affords a more understandable account of items long considered as peculiar Western achievements, including the industrial revolution and mass democratic political movements.