Member nations of the North Atlantic Treaty Organization (NATO) have observed a dramatic increase in confirmed or suspected Russian aggression, suggesting an attempt to probe any weaknesses in the alliance. While the incidents have motivated NATO members to develop better defenses against drones, they have also shown a resilient alliance with a united front, which is still committed to backing Ukraine more than three years after Russia’s invasion in February 2022.

The latest suspected airspace violations came on two consecutive nights this weekend, when multitudes of unidentified drones swarmed Danish military bases and the Copenhagen airport, shutting down all air traffic. Authorities suspect the drones may have been launched from three Russian vessels traveling past Denmark at the time; the vessels have each been sanctioned and may belong to Russia’s “shadow fleet” that evades sanctions. Denmark responded by installing scanning radar at Copenhagen airport, banning all non-military drone flights, and welcoming a German air defense frigate to a berth at Copenhagen.

“Russia has used drones for surveillance of NATO countries, especially those supporting the war in Ukraine like Poland,” said Georgetown University professor Daniel Byman. “The drones are also a form of intimidation and a way of probing air defenses.”

James Rogers, co-founder of the British International Studies Association’s War Studies Working Group, concurred. “Russia is using drones to harass and test NATO,” he explained. “Each flight is about probing defenses, mapping our responses, and reminding us of our vulnerabilities. They’re cheap, small, deniable, and hard to stop; the perfect gray-zone weapon.”

Mysterious drones were also spotted recently over a military base in Marne, France, near Norway’s Oerland Air Force Base, and near Spain’s Canary Islands. Large numbers of Russian drones operating in Ukrainian territory crossed the border into Poland and Romania, causing the NATO members to scramble air defenses. In a September 10 incident, Poland and other NATO allies actually shot down Russian drones that had crossed into Poland.

Russia’s airspace aggression is not just from drones. On September 19, Russian MiG-29 jets armed with missiles entered Estonian airspace, prompting Estonia to invoke Article 4 of NATO’s Washington Treaty, consulting with allies for the second time since the beginning of September (following Poland).

In response to the Estonian incident, NATO issued a statement to “strongly condemn” Russian aggression. Days before the latest round of incursions, NATO had already established the pattern. “Several other Allies — including Finland, Latvia, Lithuania, Norway, and Romania — have also recently experienced airspace violations by Russia.”

Of course, Russian Foreign Minister Sergei Lavrov denied that Russia had any intention of attacking NATO members. At his speech before the U.N. General Assembly last week, Lavrov accused Western nations of “increasingly common” threats against Russia, and he warned any “aggression” against Russia would receive a “decisive response.”

Last week, ambassadors from the U.K., France, and Germany attended a closed-door meeting with Russian officials in Moscow, from which they concluded that Russian commanders had deliberately chosen to violate Estonian airspace.

The seriousness of Russian airspace infractions is evident from the scale of their aerial assaults in Ukraine. Early Sunday morning, Russia launched 593 drones and 50 missiles at cities across Ukraine, the largest strike in three weeks. Thus far, Russia has only tested NATO defenses with a handful of drones, but it is unclear whether NATO countries are prepared to counter a sudden barrage of hundreds.

In fact, members of NATO’s eastern flank now plan to build a multi-layered system of air defenses to act as a “drone wall” against Russia. Estonia, Latvia, Lithuania, Poland, Romania, and Bulgaria hope that such defenses would give them low-cost options to launching fighter jets or multi-million-dollar missiles as a first response.

The planned “drone wall” in eastern Europe is not the only NATO buildup in response to Russian aggression. On Sunday, flight trackers noticed around a dozen U.S. air tankers flying across the Atlantic. The last such movement of air tankers preceded the U.S. bombardment of Iran’s nuclear weapons sites, leading some to speculate that a dramatic military operation was imminent. However, the move could simply provide NATO planes more flexibility in case of drones swarming their landing zones.

The tankers could also be headed to the North Sea, where NATO is staging a large-scale, planned training event. Recently, fighters participating in that training event (“Exercise Cobra Warrior 25-2”) flew from an aircraft carrier in the North Sea to a target at the entrance of the Gulf of Finland, a 1,000-mile journey to remind Russia that North Sea-based armaments can reach all the way to their borders. “We can fly the F-18s 1,000 miles (1,600 km), and even longer with aerial refueling. No problem [reaching] Finland,” said Capt. David J. Dartez.

Although planned beforehand, the NATO exercise has largely coincided with increased Russian aggression, which has increased significantly since the beginning of September.

The aggression also comes as U.S. President Donald Trump pivots to a harder line on Russia, speculating that Ukraine could win the war as a way to force Putin to take negotiations seriously. Trump is also considering giving Ukraine the green light to deploy U.S.-made Tomahawk cruise missiles and to launch them into Russia, giving Ukraine the capability to fire 1,500 miles into Russian territory at Moscow itself. Russia has been “fighting aimlessly for three and a half years in a war that should have taken a Real Military Power less than a week to win. This is not distinguishing Russia,” Trump said of the war.

Historians may say the Cold War ended 35 years ago, but the rivalry between Moscow and Washington remains as active as ever, with an increasingly Western-facing Europe resolved to oppose Russian aggression at every turn. NATO may need to catch up on drone technology, but they are united in their resolve to repel Russia.