It started in 1973 as something simple, not at all formal: a handshake agreement between two generals, one from the Minnesota National Guard, one from the Norwegian Home Guard. Norwegian soldiers would train in Minnesota for a couple of weeks, and Minnesota soldiers would train in Norway for a couple of weeks.

Almost 50 years later, the Norwegian Reciprocal Troop Exchange is the world's longest-running military exchange program.

This weekend's celebration of the 50-year military partnership comes at a perilous time in Europe as Russia's invasion of Ukraine heads toward a second year. Though the exchange program has brought palpable military benefits — Minnesotans learning winter warfare tactics, Norwegians training in cyber and weapons techniques — the main benefit is less tangible: understanding each other's military culture and each other's humanity, which leaders say can bear fruit during fraught geopolitical times. Military leaders here and in Norway say that's even more important as Russia's invasion of Ukraine has tested — and strengthened — ties between NATO countries.

"If you can cope with harsh military winter warfare, you can cope with anything," said Brig. Gen. Morten Eggen, chief of staff of the Norwegian Home Guard. "But we need to have a common understanding in peacetime to function during a situation as we now have in Ukraine. It's even more important nowadays to also have an exchange program from low levels up to the political level."

This month's annual Norwegian Reciprocal Troop exchange, known as NOREX, will be filled with events starting this weekend and lasting several weeks: 100 Norwegian soldiers training at Camp Ripley for combat life-saving techniques as well as an infantry simulation training exercise and a Norwegian meal at Camp Ripley for soldiers; a Twin Cities visit by the U.S. ambassador to Norway; and the signing on Saturday of a memorandum by Gov. Tim Walz to elevate this relationship to part of the National Guard Bureau's "state partnership program,"

Later, 100 Minnesota soldiers will head to Norway for winter warfare training, cultural learning and the official partnership signing ceremony attended by Gen. Daniel Hokanson, chief of the National Guard Bureau. For Minnesota soldiers, the program is often cited as a career highlight, as much for the training as for the lifelong relationships.

Cultural ties between Minnesota and Norway abound: lefse and krumkake, reservedness and modesty, the hardiness of dealing with harsh winters and the love of water that stems from 10,000 Minnesota lakes and 18,000 miles of Norwegian coastline.

Those similarities are no surprise in a state with nearly 900,000 people of Norwegian ancestry, by far the highest Norwegian American population in the United States.

"Almost every cabinet member I speak to or any person in the military here has relatives in Minnesota," said Marc Nathanson, the U.S. ambassador to Norway, whose own ancestors emigrated from Norway to Minneapolis in the 1800s. "And that's permeated into the military. There's a closeness, a commonality."

The Ukraine war, Nathanson said, has underscored the importance of these partnerships — especially with Norway, which has a 120-mile border with Russia. That is one reason the 50-year anniversary coincides with elevating the relationship to the National Guard Bureau's State Partnership Program. (That program began after the collapse of the Soviet Union to help stabilize Warsaw Pact nations and professionalize their militaries; the Minnesota National Guard has had a partnership with Croatia for more than a quarter-century.)

The program changed Mark Lappegaard's professional and personal life.

Lappegaard was a National Guard soldier studying at the University of Minnesota in the 1990s when he went to Norway. As part of the training, he skied for three days in the mountains; he slept in a snow cave; he ate at Camp Torpomoen's chow hall, where a cook spotted his name tag.

"You're from here," the cook said.

Lappegaard's family name was on a map: a nearby farm in the Hallingdal Valley. He discovered his great-grandfather had emigrated from there in 1882, such an amazing coincidence that the local newspaper wrote about it.

Back in Minnesota, a Norwegian classmate, Edel Mauritzen, translated the newspaper article for him. The two ended up getting married. During his 25 years in the National Guard, which included two tours of Iraq, he kept up his Norwegian military connections, hosting Norwegian soldiers in Minnesota and returning to Norway with the troop exchange program in 2004. In 2016, after he retired from the Guard, he and his wife moved to her Norwegian hometown, Stavanger, with their two children.

Their marriage may be the most intimate version of this program forging lasting relationships. But the connections have the same thing in common: Working across cultures has lasting benefits, in personal lives as well as during military deployments to places like Iraq and Afghanistan.

"It has this practical reason in building unit cohesion — having that appreciation of different cultures, getting over the hurdle of working with foreign militaries," Lappegaard said.

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The Norwegians will head to Camp Ripley on Sunday for a week of training. Minnesota National Guard soldiers will head to Norway soon after.

As the U.S. military has spent much of the past two decades focused on desert warfare, their skills in winter warfare have atrophied, Guard leaders said. Only a handful of active-duty U.S. bases are equipped for winter-weather training. In the aftermath of Russia's invasion of Ukraine, the U.S. military is re-emphasizing major combat operations as opposed to its recent focus on stability operations in Iraq and Afghanistan.

But more important than training, they say, are relationships.

Brig. Gen. Lowell Kruse, deputy adjutant general of the Minnesota National Guard, first participated in 2006, escorting Norwegian Home Guard leaders in the state. He traveled to Norway in 2015 and in 2017 spent a week in Minnesota with the commander of the Norwegian Home Guard, Eirik Kristoffersen. Gen. Kristoffersen is now head of the entire Norwegian military.

"He's a Facebook friend," Kruse said. "I can reach out to Eirik and have a conversation almost any time I want. The exchange at its heart is about relationships. In the military, we are a lot better off if we know who we are fighting with in the foxhole before the bullets start flying."

Correction: A previous version of this article misstated the date of the original agreement between the Minnesota National Guard and the Norwegian Home Guard.