American troops were met with waving American flags on Thursday as they arrived in Poland as a part of NATO efforts to deter Russian aggression in the region, and the Kremlin isn’t pleased about it.

A total of approximately 3,500 U.S. troops are currently being deployed to seven Eastern European nations, along with more than eighty tanks and hundreds of armored vehicles as a part of NATO’s Operation Atlantic Resolve.  This show of force is a direct response to the military annexation of Crimea by Russian forces in 2014, as well as continued tensions between Putin’s regime and those who share a border with the Russian state.

“This is the fulfilment of a dream,” said Michal Baranowski, director of the German Marshall Fund, a think tank in Warsaw, Poland. “And this is not just a symbolic presence but one with a real capability.”

American commitment to this operation was promised by now-departing U.S. President Barack Obama, as a part of a larger effort to protect and stabilize the region after fears of continued Russian expansion gripped Eastern Europe.  Now, many fear that incoming President Donald Trump will undermine the expansion of NATO defenses in the region due to his softer stance on Putin’s regime.