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Czarek Sokolowski, Associated Press
A U.S. soldier is welcomed by a Polish army official as U.S. Army vehicles cross the Polish border in Olszyna, Poland, Thursday, Jan. 12, 2017 heading for their new base in Zagan. First U.S. troops arrive in Zagan in western Poland as part of deterrence force of some 1,000 troops to be based here and reassure Poland that is worried about Russia's activity.

WARSAW, Poland — American soldiers are rolling into Poland, fulfilling a dream Poles have had since the fall of communism in 1989 to have U.S. troops on their soil as a deterrent against Russia.

U.S. Army vehicles and soldiers in camouflage crossed into southwestern Poland on Thursday morning from Germany and were heading for Zagan, where they will be based.

U.S. and other Western nations have carried out exercises on NATO's eastern flank, but this U.S. deployment will be the first continuous deployment to the region by a NATO ally.

Despite the celebrations, a cloud also hangs over the historic moment: anxieties that the enhanced security could eventually be undermined by the pro-Kremlin views of President-elect Donald Trump.

Poland and the Baltic states are nervous about Russian assertiveness displayed in Ukraine and Syria.