U.S. troops are moving into Poland as part of an ongoing mission to step up America's presence in eastern Europe.
About 3,500 U.S. personnel will spend the next nine months conducting training exercises with local security forces. They brought hundreds of tanks and armored vehicles with them.
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The plan is to rotate the U.S. brigade through other eastern European NATO member states every nine months for training exercises. NATO is also sending similar brigades around the region.
Predictably, Russia isn't thrilled. A Kremlin spokesman said the military buildup will "threaten our interests, our security."
