After having “waited a very long time,” Polish leaders gave a warm welcome to thousands of U.S. troops Saturday at a time when European countries have expressed concern about increased Russian aggression.

The U.S. sent more than 3,000 troops, along with tanks and other armored vehicles, to Poland following pressure from NATO members to better safegaurd against the threat of Russian encrouchment after the Vladimir Putin’s country took Crimea form Ukraine in 2014.