In this Oxford address, Theodore Roosevelt reflects on the shared spirit of English-speaking peoples and turns to a larger question that preoccupied the modern age: how science has changed the way we understand life, history, and civilization. He welcomes scientific rigor in the study of the past, but insists that history must remain vivid literature as well as exact inquiry, and warns against the narrowness of overconfident specialists. From there, he builds a sweeping comparison between biological evolution and human affairs, arguing that nations, like species, may arise, transform, merge, or disappear in ways both visible and mysterious. Using mammalian evolution, the horse, and the strange rise and collapse of South America's isolated fauna, Roosevelt shows how extinction can mean either total loss or transformation into new forms. He extends that insight to human history: Western Europe, Eastern Europe, Russia, the Americas, and the Roman world all reveal that "new" nations often grow from older foundations, while seeming deaths may be only absorption or continuation in altered shape. Blending history, science, and political reflection, Roosevelt offers a powerful meditation on unity, diversity, and the hidden forces that make and unmake civilizations. This edition has been fully restored with modern typesetting, custom cover design.