And the "the Soviet expansion into Eastern Europe" was the business of the US, and not Eastern Europe itself, because?
Not to mention that the US army never fought the USSR in Eastern Europe. Or that Eastern Europe was more or less divided by the allies with USSR, as if it was their own property -- and that the US occupied the western half of Germany (and Japan).
Left to its own devices, the USSR wouldn't have "eastern Europe" and couldn't afford to get it after the huge WWII cost it paid. But it was given to it, with the western allies pretending to believe BS assurances about Stalin allowing democratic elections there. It was convenient for all sides to get their grubby hands on their side (eastern/western) of the battle-torn Europe.