The movement of US troops from Germany to Poland was confirmed on Saturday at a signing ceremony in the former Communist-ruled nation.
US Secretary of State Mike Pompeo sealed the defence co-operation deal that paves the way to deploy more American troops to Poland and extend its access to Polish military bases.
Several military commands are being transferred from Germany, where they have been a key line of Nato military planning.
The shake-up also came after numerous complaints from US President Donald Trump that Germany did not spend enough on defence and its Nato commitments.
The deal signed on Saturday allows for the enhancement and modernisation of existing capabilities and facilities by allowing US forces access additional Polish military installations.
“The opportunities are unlimited, the resources will be available,” Mr Pompeo said on Saturday.
“Troop levels matter … but the world has moved on too,” Pompeo said, referring to threats posed in space, cyberspace and disinformation campaigns. He said the defence agreement would allow work on those threats too.
Polish leaders said the deal increased the security of its neighbours.
“This is going to be an extended guarantee: a guarantee that in case of a threat our soldiers are going to stand arm-in-arm,” Poland’s President Andrzej Duda. “It will also serve to increase the security of other countries in our part of Europe.”
Polish Foreign Minister Jacek Czaputowicz added that the presence of American troops “enhances our deterrence potential because we are closer to the potential source of conflict”.
“It is important that they should be deployed here in Poland and not in Germany,” he said.
About 4,500 US troops are currently based in Poland, and a further 1,000 are about to be added.
Several US military commands will be moved out of Germany, including the US Army V Corps overseas headquarters which will relocate to Poland next year.
“The agreement will enhance our military co-operation and increase the United States’ military presence in Poland to further strengthen Nato deterrence, bolster European security, and help ensure democracy, freedom, and sovereignty,” Mr Trump said in a statement.