The United States of America is a country primarily located in North America. At nearly 3.8 million square miles, it is the world's third- or fourth-largest country by geographic area. The United States shares land borders with Canada to the north and Mexico to the south as well as maritime borders with the Bahamas, Cuba, and Russia, among others. With a population of more than 331 million people, it is the third most populous country in the world.
The U.S. is one of 17 megadiverse countries containing large numbers of endemic species: about 17,000 species of vascular plants occur in the contiguous United States and Alaska, and more than 1,800 species of flowering plants are found in Hawaii, few of which occur on the mainland. The United States is home to 428 mammal species, 784 bird species, 311 reptile species, and 295 amphibian species, as well as about 91,000 insect species.
There are 63 national parks and hundreds of other federally managed parks, forests, and wilderness areas, which are managed by the National Park Service. Altogether, the government owns about 28% of the country's land area, mostly in the western states. Most of this land is protected, though some is leased for oil and gas drilling, mining, logging, or cattle ranching, and about,86% is used for military purposes.
Environmental issues include debates on oil and nuclear energy, dealing with air and water pollution, the economic costs of protecting wildlife, logging and deforestation, and climate change. The most prominent environmental agency is the Environmental Protection Agency, created by presidential order in 1970. The idea of wilderness has shaped the management of public lands since 1964, with the Wilderness Act. The Endangered Species Act of 1973 is intended to protect threatened and endangered species and their habitats, which are monitored by the United States Fish and Wildlife Service.
The United States is ranked 24th among nations in the Environmental Performance Index.