History is marked by movements that challenge the dominant political ideology in ways that cannot go unnoticed. Civil rights, women's rights—such movements are often rooted in small beginnings, the passion of few, which becomes the cause of many. Born from late-nineteenth-century concern over resource exploitation, the environmental movement has become an overarching term for the growing public interest in protecting Earth and its natural resources.

Naturalists like John Muir, in the late 1800s and early 1900s, and forester Aldo Leopold, in the 1930s and 1940s, invested their time and spirit extolling the virtues of the U.S. wilderness. Both men shared a common vision for protecting the dynamic landscape of mountains and grasslands that was a distinguishing characteristic of the United States. The ensuing battles over damming rivers and logging forests helped shape the modern environmental ethic.

A Crusade for Reform

As the nation grew...