This is part two of a series examining the challenges confronting the NATO alliance.

POLAND-BELARUS BORDER — Riding in a military convoy escorted by armored vehicles from Poland’s 18th "Iron Division" along the country’s 521-kilometer border with Belarus, soldiers pointed toward dense forests where they say Europe’s newest form of warfare is unfolding.

Polish officials warn illegal migrants weaponized by Russia and Belarus to destabilize NATO's eastern flank are also making their way to the United States — part of what Warsaw calls an ongoing war against the Western alliance that has direct implications for American security.

The border was once guarded mainly by Poland’s Border Guard and police. But after years of mounting pressure from illegal crossings, Polish officials say the army was deployed because the situation became too large and too dangerous to handle as a conventional immigration challenge.

TROOPS AT THE BORDER: HOW THE MILITARY’S ROLE IN IMMIGRATION ENFORCEMENT HAS EXPLODED UNDER TRUMP

Now, the frontier is guarded in layers: soldiers, border guards and rapid-response forces. A temporary barrier built in 2021 has become an electronic fence backed by surveillance systems and military patrols. Polish officials say migrants trying to cross have come from countries including Syria, Somalia, Afghanistan and India.

They describe the crisis as "artificial migration," saying the illegals are flown into Belarus from the Middle East, Africa and Asia and then transported toward the Polish border by Belarusian authorities in an effort to pressure and destabilize NATO countries.

Military officials at the border said the peak was in 2021, when there were 39,697 illegal crossing attempts. By 2025, it was 29,869, slightly fewer than in 2024. So far in 2026, they have seen a major drop, they say.

For Warsaw, the numbers tell only part of the story.

Polish officials say the border pressure is not spontaneous illegal migration, but a Russian-backed Belarusian operation designed to destabilize NATO from within.

"We are at war," Ambassador Krzysztof Olendzki of Poland’s Foreign Ministry told Fox News Digital after the border visit.

"Not only Poland, but also all the countries of the eastern flank of NATO, we are in war," Olendzki said. "We cannot see it as a classical war with soldiers, with tanks and so on, but the war is exercised by our adversaries, by Belarus and Russia, who are using practically migrants as an asymmetric weapon against NATO countries."

WHITE HOUSE ROADMAP SAYS EUROPE MAY BE 'UNRECOGNIZABLE' IN 20 YEARS AS MIGRATION RAISES DOUBTS ABOUT US ALLIES

The crisis dates back to 2021, when Poland, Lithuania and Latvia accused Belarusian President Alexander Lukashenko’s regime of encouraging migrants from the Middle East, Africa and elsewhere to travel to Belarus and cross illegally into the European Union. Belarus has denied orchestrating the flows, but Poland and the EU have described the campaign as hybrid warfare.

Olendzki said the goal is not only to push people across the border, but to create chaos inside Western societies.

The border visit underscored how far Poland has gone to harden what it views as one of NATO’s most vulnerable frontiers.

Capt. Angelika Korkosz of Poland’s 18th Division described the day-to-day strain on soldiers stationed there.

"Many times soldiers were faced with aggression from illegal groups of immigrants, and they have to act appropriately and calmly in accordance with the law and procedures while protecting themselves," Korkosz told Fox News Digital.

POLISH GOVERNMENT PLANS MANDATORY MILITARY TRAINING FOR ADULT MEN

Polish officials said migrants have used Molotov cocktails in at least two incidents, sparking fires near the border. Soldiers also spoke of a Polish serviceman who died after being stabbed by an illegal migrant at the frontier.

Korkosz said the challenge is not only violence, but exhaustion.

"A few months ago, we had minus-20-degree winters, so 12-hour duty during these conditions is really demanding," she said. "Many soldiers are here for a long time, and it is getting more and more difficult, this long separation from their relatives."

Still, she said the troops are prepared.

"The training includes decision-making under pressure in an ambiguous operational environment," Korkosz said. "That’s why when we are here at the border, we are really well-prepared for performing our duties."

Poland says the border defenses are working. Amb. Olendzki said the lower number of crossings this year reflects the physical barrier, the increased effectiveness of the Border Guard and the military presence. But he warned the threat has not disappeared, only shifted.

NATO WARNS RUSSIA AFTER POLAND SHOOTS DOWN 'HUGE NUMBER' OF DRONES THAT VIOLATED ITS AIRSPACE

"Seeing the fact that the Polish-Belarusian border is quite well guarded, our adversaries are just pushing migrants through the borders of our neighboring countries," he said. "So it hasn’t ended, but it’s changed the direction. The threat still exists, and we must be vigilant."

That matters to NATO because Poland’s border with Belarus is not only Warsaw's border. It is also the eastern edge of the European Union and NATO territory.

Belarus is Russia’s closest ally and allowed its territory to be used for Russia’s 2022 invasion of Ukraine. Ukrainian President Volodymyr Zelenskyy warned Russia may be trying to pull Belarus deeper into the war and could use Belarusian territory to threaten Ukraine or even a NATO country.

That fear is central to Poland’s security posture.

During a meeting with reporters in Warsaw, Polish Foreign Minister Radosław Sikorski told Fox News Digital Russia’s war against Ukraine is, for Poland, "a matter of national safety and existence."

But Sikorski said the threat to NATO countries is already wider than the battlefield in Ukraine.

"We had on NATO countries’ territories assassinations, numerous drone attacks on airports, on critical infrastructure," Sikorski said. "We had very serious cyberattacks."

Sikorski said Poland faced a Russian-instigated cyberattack last December on critical energy infrastructure that Warsaw believes was intended "to black out part of Poland."

The warning fits a broader pattern of concerns across NATO’s eastern flank. The Associated Press reported earlier this year that balloons from Belarus had crossed into Polish airspace for a third consecutive night, with Polish forces describing the incidents as attempts to test air defense responses.

For Poland, illegal migration, cyberattacks, drones, sabotage and disinformation are not separate problems. They are different pieces of one Russian and Belarusian pressure campaign against NATO.

Olendzki said Poland’s role is to stop the pressure before it moves deeper into Europe or beyond.

"Standing on guard on the eastern flank of NATO, we are providing security not only to Poland, to Lithuania, Latvia, Estonia, Finland, but to entire NATO, also to the United States," he said.

That U.S. connection is a central part of Poland’s message to Washington: The eastern flank is not a distant European problem, but a front line in a broader confrontation with Russia and its allies.

Poland now spends nearly 5% of its GDP on defense, the highest rate in NATO, if based on GPD. Sikorski said Warsaw has long taken defense spending seriously.

"We never went below 2% defense spending," Sikorski said. "Now we are spending almost 5%. This is real military spending."

He said the eastern flank has become more influential inside NATO because countries closest to Russia were proven right.

US ALLIES ACCUSE RUSSIA OF 'ESCALATING HYBRID ACTIVITIES' AGAINST NATO, EU NATIONS AFTER DATA CABLES SEVERED

"The eastern flank is much more powerful than even five years ago," Sikorski said. "We were right about the nature of Putin’s regime and Russia’s aggressive strategy."

That view has shaped Poland’s approach to the United States. Warsaw wants American troops to remain in Europe, but Polish officials also acknowledge that Europe must assume more of the defense burden as U.S. attention increasingly shifts toward China and the Indo-Pacific.

Sikorski said Poland understands that "Europe ceased to be angle number one for U.S. foreign policy," but wants any change in America’s role to be "gradual and well-designed."

He added that Poland wants the shift in trans-Atlantic security to be "not a divorce, but a new kind of relationship."

For now, that relationship is being tested along a cold, wooded border where Poland says NATO’s future wars may already be taking shape.

The Polish soldiers patrolling the frontier do not describe their mission in grand geopolitical terms. Korkosz said she joined the military because she wanted to do "something which matters."

But to Polish officials, the mission at the Belarus border is much bigger than immigration enforcement.

It is a warning to the rest of NATO that the alliance’s next war may not begin with tanks crossing a border, but with migrants pushed through forests, cyberattacks on power grids, drones near airports and disinformation campaigns designed to fracture societies from within.