1900s: Americans recognize the need for conserving or protecting the environment. The U.S. government begins forest preservation efforts in 1891. In 1892 John Muir founded the Sierra Club. In 1903 President Theodore Roosevelt created the National Wildlife Refuge System.

Today: The Sierra Club still exists and is a major force in the environmentalist movement. Business and environmentalists clash frequently over America's natural resources and endangered species.

1900s: Indigenous to the area, wolves inhabit most of the northwestern United States, Canada, and Alaska.

Today: Wolves have long ago disappeared from most of the United States. A project to reintroduce wolves to Yellowstone National Park is hotly contested by local ranchers, but is implemented with some success in the 1990s.

1900s: Alaska, which became part of the United States in 1867, was sparsely populated until the gold rushes in Juneau (1880) and the Klondike (1897). The excitement regarding these discoveries brought...