PLATTSBURGH, N.Y. — The path from American isolationism to internationalism passed through British Guiana (the boundary dispute of 1895-1899), Havana Harbor (the explosion of the battleship Maine), Manila Bay (Commodore George Dewey’s defeat of the Spanish naval force), Nanking (the negotiations over the Open Door Policy) … and Plattsburgh, New York.

Plattsburgh?

This city of 19,360 planted on the northwestern shore of Lake Champlain has a virtually unknown but vitally important role in American history. A mere 22 miles from America’s northern border, it is both the gateway to Canada and the gateway to American international involvement — and there is a direct line between what happened here in the years before World War I and the military doctrine espoused by American presidents from George Washington to Joe Biden.

When Ronald Reagan told the 1980 Republican National Convention that “we know only too well that war comes not when the forces of freedom are strong, but when they are weak,” he expressed a thought with roots in the shale and limestone prominent in this region or, more precisely, on the grassy expanse that comprises the parade ground known here simply as “The Oval.”

It was here, on a vast plain, that hundreds of young Americans — plus four members of the Roosevelt family and Gen. Leonard Wood, renowned as governor general of the Philippines and chief of staff of the Army — gathered for summer military training. The country was still years from entering the Great War, known today as World War I. President Woodrow Wilson was preparing to run for reelection on the slogan “He kept us out of war.” And yet here, preparation for war began.

“This contributed an enormous amount because those who came here learned how to become soldiers in the event of eventual war,” said Anastasia Pratt, the Clinton County historian and chair of the historical studies department at SUNY Empire State College. “This shows us the country was moving away from the sense we could isolate and be uninvolved in world affairs. We became active players around the world, and this was the first element of that.”

The program became known as the Plattsburg Idea — like Pittsburgh, Plattsburgh for a time lost its final “h” — and there was a lot of work to be done. The country’s Army stood at 98,000 troops, with a total force including reserves that was smaller than that of Greece and Bulgaria; by contrast, Russia had a standing army and reserves of 5.97 million. Gen. Charles Summerall, who commanded the 1st Infantry Division during World War I and would become chief of staff of the Army and, for more than two decades, the president of The Citadel, said that the training at Plattsburg “formed the backbone of the new army.”

The beginning was modest. “If you are an affluent college-age male, you can spend your summer at camp — boot camp,” the recruiting literature said. “Through the 90 days you will be awakened by bugle calls and spend your days doing drills, calisthenics and learning other military duties.”

The camp ended with a mock battle lasting several days. That hardly replicated real conditions. The Battle of the Somme lasted 141 days in 1916, and the British had 57,470 casualties on the first day of fighting alone.

Plattsburg was chosen because former President Theodore Roosevelt, a strong advocate of military preparedness, knew this part of the world. It possessed two important attributes: It was sparsely populated, and it offered possibilities for training for any kind of war except desert combat.

It also was steeped in American military history. Long before the area was the site of an Army base, an Army college and an Air Force base that was part of the Strategic Air Command, this region had been a training site for soldiers. Here they marched and drilled as early as the beginning of the 1800s. American Maj. Gen. Wade Hampton’s army occupied Plattsburgh during the War of 1812. Two large stone barracks were built in the 1830s, and in the pre-Civil War years, soldiers trained here.

But its greatest contribution was as a site for men, as the advertisements in Collier’s and The Saturday Evening Post put it, to “give your vacation to your country and still have the best vacation you ever had.” The United Cigar Stores, then a national chain, sponsored posters proclaiming that “the Minute Men of today are going to Plattsburg.” Spinoffs abounded. Franklin Delano Roosevelt, then the assistant secretary of the Navy, supported a series of Naval Plattsburg training cruises. Once war broke out, 16 Plattsburg Camps were established around the country.

In the pages of The Plattsburger, a yearbook for veterans of the second summer of Plattsburg training, is a tribute to the preparedness movement. “If the world is to be made safe for democracy,” according to the book, “it is the Plattsburg idea that a democratic army must do it.”

And yet, this slender slice of American history has been largely forgotten.

“For years and years, I never heard a word about it,” said Penelope Clute, a former city court judge who moved to Plattsburgh 44 years ago. “It’s not present in people’s minds. People know about the 1814 Battle of Plattsburgh, but nothing about what happened here a century later.”

After World War I, the Plattsburgh post hospital became a center for the treatment of “shell shock.” And in the years before World War II, Nazi Germany, Japan and more than a dozen other nations sent delegations here to view training sessions. They observed maneuvers of the 1st Army as late as four days before the outbreak of World War II.

In 1916, while the United States resisted entering World War I, a song developed in the camp that finally found its way into broader popularity and promoted the training undertaken at Plattsburg. Its lyrics included this passage:

March on to Plattsburg, Swing into line and hike away

There’s one place for us and that’s Plattsburg

One time and that’s today.

March on! Ev’ry road leads to Plattsburg,

Under the Flag, Glorious Flag, The Red, White and Blue!

In his first annual address to Congress, the precursor to the modern State of the Union Address, Washington said that “to be prepared for war is one of the most effective means of preserving peace.” Today nobody sings “On to Plattsburg,” but national preparedness is part of the American credo. Thank Plattsburgh for that.

(David M. Shribman is the former executive editor of the Pittsburgh Post-Gazette.)