The United States took a bold step toward growing and protecting the world's largest park system when President Woodrow Wilson signed into law the National Park Service Organic Act on this day in history, August 25, 1916. 

The act most notably created the National Park Service, "a new federal bureau in the Department of the Interior responsible for protecting the 35 national parks and monuments then managed by the department and those yet to be established," according to the service's own official history. 

The NPS today manages over 400 protected reservations in all 50 states, while welcoming about 300 million visitors per year. 

It employs about 20,000 people. 

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The United States established the world's first national park under President Ulysses S. Grant on March 1, 1872, with the Yellowstone National Park Protection Act. 

Yosemite, Mount Rainier and Crater Lake national parks soon followed. 

Yellowstone National Park sign

A sign at the south entrance of Yellowstone National Park, Wyoming, courtesy of the National Park Service, Department of the Interior, circa 1965. (Archive Photos/Getty Images)

The nation was in a frenzy to protect its vast wilderness and historic sites. 

But there was a problem. 

The National Park Service manages over 400 protected reservations while welcoming about 300 million visitors per year.

"Although more than a dozen national parks had been designated by [1916], along with 30 national monuments, the areas functioned with little oversight," National Geographic reported in 2015. 

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"Opportunists hungry for the parks’ natural resources took advantage. Poachers targeted the plentiful wildlife."

President Woodrow Wilson

Woodrow Wilson (1856-1924), president from 1913-1921, goes over papers as his second wife, Edith Bolling Galt Wilson (1872-1961) looks on.  (Stock Montage/Getty Images)

National Geographic added, "San Francisco boosters even convinced Congress to allow Yosemite's Hetch Hetchy Valley to be flooded as a reservoir for the city’s residents."

The Organic Act was intended to resolve those issues by bringing greater management to the system. 

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It gave the National Park Service a dual mission, notes the Department of Justice's Environment and Natural Resources Division, "both to conserve park resources and provide for their use and enjoyment ‘in such a manner and by such means as will leave them unimpaired’ for future generations."

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The U.S. National Park system today covers about 133,000 square miles.

It's about the size of the nation of Germany — and larger than Poland, Italy or the United Kingdom. 

Wizard Island on Crater Lake

Crater Lake National Park, Oregon, is one of America's oldest national parks. Wizard Island, Crater Lake, from Discovery Point.  (Bernard Friel/Education Images/Universal Images Group via Getty Images)

Combined, America's national parks are larger than 170 of the 234 nations in the world. 

"The Organic Act is one of this country’s most important statutory directives addressing the protection of our natural and cultural heritage," former NPS deputy director Stephen Martin told congressional lawmakers in 2005. 

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"The National Park System, established by the Organic Act, is often cited as ‘the best idea America ever had,'" Martin added, "and has been described by President Bush in a proclamation for National Parks Week as ‘America’s gift to the world.’"