The United States was alarmed by Soviet control of Eastern Europe at the end WW II because officials believed Soviet expansion would not stop at Eastern Europe.
Step-by-step explanation:
The Grand Alliance, otherwise called The Big Three, was a military union comprising of the three significant Allies of World War II: the Soviet Union, the United States, and the United Kingdom. Relations between the Soviet Union and the United States were driven by a perplexing exchange of ideological, political, and monetary elements, which prompted moves between wary collaboration and frequently severe superpower contention throughout the years.