“Balutan! You’ve got to balutan!”

Anthony Mantanona — Uncle Tony, Guam’s favorite Indigenous baker — pointed to trays of fresh coconut bread, reminding the barbecue’s departing guests to follow one of Chamorro culture’s elemental tenets: Balutan, or grab a to-go plate, be generous, be grateful, share.

“If you don’t need much, give it to someone else,” he yelled.

The Chamorro people were Guam’s first inhabitants, and through 500 years of colonization by Spain, Japan and, most recently, the United States, they have survived by sharing their land, sea and sky while holding fast to core cultural values.

Now, the Chamorro way is again being tested, as another round of encroachment by the U.S. military comes just as new efforts are being made to strengthen Guam’s Indigenous bonds.

The barbecue was being held in the backyard of a 1950s ranch-style house that doubles as a cultural center. Mr. Mantanona was baking in an outdoor oven, as children practiced speaking Chamorro and community leaders welcomed friends and curious newcomers.

In the air, American F-15s roared past every few minutes, their noise, markings and speed a reminder of the dangerous world that continues to make demands on Guam’s people.

Roughly a third of the island has been under Defense Department control for decades. But with China and the United States locked in a bitter contest for strategic advantage, Guam — a volcanic outcrop the size of Chicago, with 168,000 people — has become an even more vital military launchpad.

Adding to the 22,000 U.S. troops already here, another 5,000 Marines will soon move into a new base named after Brig. Gen. Vicente T. Blaz, the first Chamorro to become a Marine Corps general officer.

A few miles away, a pier for nuclear-powered submarines is being upgraded. More than a dozen sites have also been identified as potential locations for missile defense systems, while Andersen Air Force Base has plans for a new weapons complex.

On-island, as they say here, off-island challenges are invading once again.

Surprisingly perhaps, the heavy buildup has not created much fear. Guam’s inhabitants have known for years that their home could be a target. It’s in missile range of regional adversaries, far closer to China and North Korea than Honolulu.

But especially among Chamorros, who are Guam’s largest ethnic group, the risk of war and the U.S. military’s plans have reinforced divided identities.

Guam swims in a murky pool of Americanism. It has one of the U.S. military’s highest rates of recruitment, with Chamorros heavily represented in the ranks, but even the most decorated veterans have little say in what the federal government does on the island. It is an unincorporated territory without full representation in Congress. Its residents cannot vote for president, and while there is an elected local government, Guam remains more garrison than state; the island was handed to the U.S. Navy after the Spanish-American War in 1898.

As the author and lawyer Julian Aguon has put it: “Militarism is normalized on Guam. It’s part of our meat and drink. It’s a protein we have to work very hard to break down.”

For Suruhana Rosalia Fejeran Mateo, or Mama Chai, an 87-year-old traditional Chamorro healer, the steady creep of militarization still brings new surprises. Recently, when she trekked to a remote beach to collect plants for treating ailments, U.S. marshals confronted her, warning that she had wandered into a no-go zone.

They did not say why the beach was off-limits, said Vinessa Duenas, 26, an apprentice who was with her, learning the old ways. Mama Chai saw the interference as a bizarre reminder of the island’s dissociation from its ancient culture.

“We’re not destroying the area,” she said. “We’re just taking medicine.”

At a beach near Naval Base Guam, Ron Acfalle ran his hand along a narrow wooden canoe with a turtle and other Chamorro imagery on its hull. Once in the water, the canoe will have a triangular sail — a sight first seen and praised by Spanish explorers who reached Guam in 1521.

The colonizers called them “flying proas” and later destroyed the boats to keep people from fleeing, trading with other islands, or planning a revolt. It was the beginning of Guam’s role as a strategic international outpost.

Now students of Indigenous science are learning how to sail and navigate with the stars.

“The whole idea was to bring back what our ancestors had left behind,” said Mr. Acfalle, 64, a homebuilder and co-founder of Ulitao, a nonprofit seafaring organization. “To recreate the design that was recognized by the Europeans as one of the fastest canoes they’d ever seen.”

Smiling with pride, he said he had returned to Indigenous culture slowly. He grew up being taught that America had liberated his people from the cruel Japanese troops who seized Guam in 1941. He and his relatives were like General Blaz and many others: They chose to be grateful after the Americans returned in 1944 with a military presence.

But over time, they saw their language fade, with few asking why learning Chamorro was discouraged. Guam’s children weren’t taught local history when Mr. Acfalle went to school. They ate American foods. They fought in Korea, Vietnam, the Middle East, hoping the United States would love them back, only to find that most Americans barely knew Guam existed.

And at home, the land became littered with ordnance, the sea with spills of heavy oil.

“I’m a former Marine, you know, back in the ’70s,” Mr. Acfalle said. “I come home and I’m fighting what the military has been doing to our people.”

He connected with others in the community through a Chamorro dance group, and raised his six children to respect their roots even as one of them joined the military, too. He started studying ancient seafaring and now has become part of a loose network of Chamorro leaders — including Mr. Mantanona — who have channeled their concerns about Guam into cultural preservation and promotion.

“People want more,” Uncle Tony said.

The history of Guam is now a regular feature of the island’s high school curriculum. A new museum, with Chamorro words carved into the facade, opened a few years ago, and paddling in traditional outrigger canoes is an increasingly popular sport.

But even in renaissance, risk swirls through the Guam air. At the barbecue, as the jet engines raged above ringing cellphones and a speaker blaring Steely Dan, three bursts on a conch shell rang out.

A 9-year-old boy in a baseball uniform with dirt on his knees, chest and somehow his back stood between a garden and a view of waves crashing whitewash onto a shallow reef. A slugger for sure, he’d just come from the diamond of America’s favorite pastime when his mother asked him to explain why he had blown the three bursts from the shell.

“Sky, sea and land,” he said, in Chamorro and English.

It was a call to the ancestors, asking for protection.