NATO members are continuing their biggest combat exercises of 2025, testing their ability to rapidly deploy large-scale forces on the 32-nation alliance's eastern border as worries grow over its most powerful member, the United States.
The drills in Romania, which borders Ukraine, come as a shaken Europe grapples with a new US course under President Donald Trump.
In the run-up to the third anniversary of Russia's full-scale invasion of Ukraine, the Steadfast Dart 2025 exercises comprise about 10,000 military personnel from nine nations as part of NATO’s new Allied Reaction Force.
They are taking place over six weeks in Romania, Bulgaria and Greece.
Defence Secretary Pete Hegseth has demanded that allies dramatically ramp up military spending and said US security priorities lie elsewhere, casting doubts on Washington’s longstanding security guarantees provided to Europe.
Although the Trump administration has not announced plans to pull US forces from the region, Hegseth's remark that "European allies must lead from the front" left NATO partners contemplating a potential new reality in which the US is no longer the powerful, nuclear-armed backstop for the continent’s security.
Radu Tudor, a defence analyst in Bucharest, said a US rollback of its military presence in Romania would be "a gift" to Russian President Vladimir Putin.
"The whole eastern flank of NATO (would) become weaker in front of Russia's aggressive behaviour," he said, adding that it would push Romania to ask NATO allies to contribute troops and weapons to plug the gap left by several thousand American troops.
Admiral Stuart B. Munsch, commander of the Allied Joint Force Command, said threats to NATO "have become increasingly complex and unpredictable" over the past decade.
"To address this complex security environment, NATO has undergone a significant war-fighting transformation. We have taken our defensive plans from concept to reality," Munsch told reporters at the training base on Wednesday.
"This exercise…represents the culmination of our efforts and the beginning of our new force that will defend every inch of alliance territory."
European allies have also expressed concern over being sidelined from talks between US and Russian diplomats on Tuesday in Saudi Arabia on working towards ending the war in Ukraine.
The fast-moving developments prompted France's President Emmanuel Macron to convene select EU countries and the UK for emergency talks this week in Paris.
NATO bolstering eastern flank
This week's combat exercises in Romania saw live-fire training and trench warfare drills.
Greek and Spanish marines led exercises in Greece last week, including a mock amphibious assault.
NATO's new Allied Reaction Force, established last July, is designed to deploy at scale within 10 days and combines conventional forces with cyber and space-based technologies.
Britain leads the operation with 2,600 military personnel and 730 vehicles.
The drills also include Romania, Bulgaria, France, Greece, Italy, Slovenia, Spain and Turkey and involves 1,500 military vehicles, more than 20 aircraft and more than a dozen naval assets.
After Russia launched its full-scale invasion of Ukraine on 24 February, 2022, NATO bolstered its presence on Europe's eastern flank by sending additional multinational battlegroups to Romania, Hungary, Bulgaria and Slovakia.
Since then, Romania has played an increasingly prominent role in the alliance.
It has donated a Patriot missile system to Ukraine and opened an international training hub for F-16 jet pilots from allied countries, including Ukraine.
