What led to the unraveling of the alliance between the Soviet Union and the United
States?
The U. S. was upset that Stalin initially signed a non-aggression pact with Hitler
and Germany in 1939.
The Soviet Union was upset that the U. S. did not invade German-occupied
Europe quick enough once they joined the war effort.
The death of FDR, who was a close ally and friend of Stalin, led to tensions
between Stalin and FDR's successor, Harry Truman, who was a strong anti-
communist.
All of the above