States began in the late 19th century, out of concerns for protecting the natural resources of the West, with individuals such as John Muir and Henry David Thoreau making key philosophical contributions. Thoreau was interested in peoples' relationship with nature and studied this by living close to nature in a simple life. He published his experiences in the book Walden, which argues that people should become intimately close with nature. Muir came to believe in nature's inherent right, especially after spending time hiking in Yosemite Valley and studying both the ecology and geology. He successfully lobbied congress to form Yosemite National Park and went on to set up the Sierra Club in 1892. The conservationist principles as well as the belief in an inherent right of nature were to become the bedrock of modern environmentalism. However, the early movement in the U.S. developed with a contradiction; preservationists like John Muir wanted land and nature set aside for its own sake, and conservationists, such as Gifford Pinchot (appointed as the first Chief of the US Forest Service from 1905 to 1910), wanted to manage natural resources for human use. 20th century In the 20th century, environmental ideas continued to grow in popularity and recognition. Efforts were beginning to be made to save the wildlife, particularly the American bison. The death of the last passenger pigeon as well as the endangerment of the American bison helped to focus the minds of conservationists and popularize their concerns. In 1916, the National Park Service was founded by U.S. President Woodrow Wilson. Pioneers of the movement called for more efficient and professional management of natural resources. They fought for reform because they believed the destruction of forests, fertile soil, minerals, wildlife, and water resources would lead to the downfall of society. The group that has been the most active in recent years is the climate movement. The U.S movement began to take off after World War II, as people began to recognize the costs of environmental negligence, disease, and the expansion of air and water pollution through the occurrence of several environmental disasters that occurred post-World War II. Aldo Leopold published A Sand County Almanac in 1949. He believed in a land ethic that recognized that maintaining the "beauty, integrity, and health of natural systems" as a moral and ethical imperative. Another major literary force in the promotion of the environmental movement was Rachel Carson's