“National parks are the best idea we ever had,” Western writer Wallace Stegner once said. “Absolutely American, absolutely democratic, they reflect us at our best, rather than our worst.”

That idea, as old as the United States itself, was simply this: that the most beautiful mountains, fields, forests, and shorelines should be preserved for the enjoyment of all people. In Europe, the choicest land parcels were the province of the nobility. Americans didn’t have queens or kings—or crown jewels to protect. But we had Yellowstone and Yosemite and the Grand Canyon and Acadia seashore—and many more natural splendors.

So these became our crown jewels.

Americans enjoy their birthright, as do citizens of the world. Yosemite National Park will register some 4 million visitors in 2016. A similar number will observe the geysers and grizzlies of Yellowstone. These are near record highs, and attendance is robust in all 59 national parks, a fitting trend in 2016, which is the National Park Service’s centennial.

The law creating the park system was signed 100 years ago this week by President Woodrow Wilson. At the time, 35 national parks and monuments were under government protection, and Congress anticipated adding more.  From the beginning, though, it was always about more than majestic mountains, tall trees, and pretty waterways. The national parks tell the American story, with its conquests and conflicts: Who deserves to share this land? How should we treat its plants and animals—and how do we treat each other? For answers to these cosmic queries, we look to our parks.

President Ulysses S. Grant signed the Yellowstone Act of 1872, designating the Yellowstone region as a public “pleasuring-ground” to be preserved “from injury or spoilation, of all timber, mineral deposits, natural curiosities, or wonders within.”

Eight years earlier, however, while Gen. Grant still wore his muddy Army boots during the siege of Petersburg, his commander-in-chief, Abraham Lincoln, signed legislation laying claim on behalf of the state of California to the area that would become Yosemite National Park.

Among those who would make a pilgrimage to Yosemite’s waterfalls and forests were Theodore Roosevelt. And after spending his first night in a Yosemite sequoia grove, TR enthused: “It was like lying in a great solemn cathedral far vaster and more beautiful than any built by the hand of man.”

John Muir, Roosevelt’s friend and fellow conservationist, used a similar metaphor while arguing against a proposed dam on Yosemite’s Tuolumne River that would flood the scenic Hetch Hetchy Valley. “No holier temple,” he wrote, “has ever been consecrated by the heart of man.”

Muir would lose this battle. Hetch Hetchy’s dam was built—San Francisco needed the water—and the scenic valley flooded. But Muir won the war. Out of this fight emerged the Sierra Club, along with a national realization that when it came to the great questions of land use, there were always two sides to the equation, or more. Profound questions about American race relations have also been tackled in the national parks. They still are.

In 1830, William Clark made a return visit to the lands of the upper Missouri River. He’d first gone there at Thomas Jefferson’s behest, accompanied by his co-captain Meriwether Lewis. This time, he took along a Pennsylvania-born painter named George Catlin. His portraits of some 18 Native American tribes were shown all over the East. Some of those paintings are all that remain of once-proud civilizations such as the Mandans, an agrarian tribe that hosted Lewis & Clark in their lodges in the Corps of Discovery’s first winter in the Upper Missouri.

George Catlin become an advocate for native people, and the land they occupied, which to him were one and the same. “Nature has nowhere presented more beautiful and lovely scenes, than those of the vast prairies of the West,” he wrote in a letter published in 1841. But he feared it would soon be gone. To preserve it, he proposed the creation of a “nation’s Park” created “by some great protecting policy of government.”

In 1845, Caitlin published his second acclaimed volume, this one including one of his most famous drawings, “Buffalo Bull Grazing,” depicting a noble animal that few whites and no Indians could imagine would soon be on the road to extinction—unless they had a place that was protected.

The history of the National Park Service, like the history of the United States, didn’t march in an unbroken line. By the early 20^th century, park service rangers had exterminated the northern gray wolf from Yellowstone. Rangers trapped wolves, shot them, gassed them in their dens, clubbed them to death until they were all gone.

By the 1990s, however, Congress appropriated money for a request by the National Park Service and U.S. Fish & Wildlife biologists to reintroduce wolves to the park. It was a labor of love. Mollie H. Beattie, the first woman to head Fish & Wildlife, participated in the effort. Beattie died in 1996, as the initiative was taking off, but not before a friend noticed her rubbing cool water of the belly of a young wolf in Yellowstone to calm the animal before it could be released into the wild. Despite battling cancer, and despite the cold April rain in her face, Beattie smiled and said, “Any day I can touch a wild wolf is a good day.”

In this way, and a thousand others, we work out the great national questions of our past and future in the national parks. 2016 is not only the Park Service’s centennial, it is also the 50^th anniversary of the National Historic Preservation Act of 1966, when greatly expanded the agency’s role in evaluating and preserving the nation’s historic and archeological sites. With that responsibility has come additional ones for interpreting the American Story to those who visit the parks and national and cultural historic sites.

“What happened here?” visitors want to know. “What does it mean?” Can an agreed-upon story that unites Americans, rather than divides them, be imparted by a government bureaucrat in a Smokey-the-Bear hat? It’s a tall order for National Park Service rangers and interpretative historians—as it is for U.S. presidents.

In 1938, Franklin Roosevelt confronted this dilemma at the 75^th anniversary of the Battle of Gettysburg. In the throes of the Great Depression and with war clouds gathering in Europe, FDR saw his role as one of Reconciler-in-Chief. Some two dozen veterans of the battle, men in their 90s, made the trek to the hallowed ground in Pennsylvania. Across a stone wall at The Angle, these former enemies shook hands.

“Lincoln spoke in solace for all who fought upon this field; and the years have laid their balm upon their wounds,” Roosevelt said that day. “Men who wore the blue and men who wore the gray are here together, a fragment spared by time. They are brought here by the memories of old divided loyalties, but they meet here in united loyalty to a united cause which the unfolding years have made it easier to see. All of them we honor, not asking under which flag they fought then—thankful that they stand together under one flag now.”

Strictly speaking, what Roosevelt said about Lincoln wasn’t true. Lincoln spoke as commander-in-chief of the Union Army when he delivered the Gettysburg Address. But Roosevelt’s larger point about unity was what the historical moment demanded on the eve of the Second World War. Today, in the wake of Ferguson and Dallas, Americans are less willing to sweep the underlying cause of the Civil War under the tattered carpets of time.

If the Civil War was really about slavery, we expect National Park Service historians to tell us that. At Arlington National Cemetery, a stately mansion overlooks the grounds. This is where Robert E. Lee lived and made his fateful decision to go to war against his country. Fields where slaves once labored now hold the graves of 400,000 military veterans and their loved ones, veterans who fought for freedom.

As at Yellowstone and Yosemite, some 4 million people will traverse these grounds this year. Those gravestones, and the remnants of the slave quarters adjacent to the Lee house, are all part of the same story, one which is still unfolding. In an era of enormous annual government budget deficits, the national parks may seem a luxury. They aren’t. As Mollie Beattie once said in describing the parks, “What a country chooses to save is what a country chooses to say about itself.”