NATO defense minister have agreed to station four battlegroups in the Baltic states and Poland to guard against Russian aggression in the region.

Britain, Canada, Germany and the United States would each send some 800 soldiers to protect the three Baltic nations as well as the narrow strip of land around the city of Suwałki that connects Poland and Lithuania.

Kaliningrad, Russia’s Baltic Sea enclave, lies to the northwest and Belarus, Russia’s closest ally, borders Lithuania and Poland to the south and east, respectively.

The plan falls short of Eastern European requests for permanent NATO bases in the region but still marks “the biggest reinforcement of our collective defense since the end of the Cold War,” said Secretary General Jens Stoltenberg.

Tripwire

The European and North American troops would act as a “tripwire,” leaving Russia in no doubt that the West will respond if it invades one of its former satellite states.

A new 5,000-strong rapid reaction force would be on standby to help the troops in Eastern Europe if needed.

“They will not be left out to dry,” said Michael Fallon, the British defense secretary.

Russian specter

Russia has tested the alliance’s readiness in recent years by flying warplanes near or through its airspace.

It also alarmed Eastern European nations when it annexed the Crimean Peninsula from Ukraine in 2014.

Tomasz Szatkowski, Poland’s deputy defense minister, recognized that a few thousand more troops cannot on themselves defend the eastern theater. “This is something that will provide a significantly more credible deterrent,” he said.

His government last year asked for permanent NATO bases in Poland, similar to the ones in Germany, Italy and the Netherlands.

The West, sensitive to Russia’s fear of encirclement, has shied away from building military bases in the former East Bloc nations that joined NATO after the Cold War.