More than anything else, the Soviet Union wanted the United States to recognize its security concerns and sphere of influence in Eastern Europe. The Soviet Union was concerned about the possibility of an invasion from the West, as it had been invaded several times in the past. As a result, the Soviet Union sought to establish a buffer zone in Eastern Europe that would protect it from potential invasions. The United States, on the other hand, saw this as an expansionist move by the Soviet Union and sought to contain Soviet influence through policies such as the Truman Doctrine and the Marshall Plan.