Final answer:
Americans feared the spread of communism would threaten their way of life.
Step-by-step explanation:
The reason why Americans worried about the growth of communism in Eastern Europe and China during the time of 'McCarthyism' is because they feared that the spread of communism would threaten their way of life.
This fear was primarily due to the ideological differences between the United States and the Soviet Union/China. The United States favored capitalism and democracy, which they believed would improve human life and provide freedom. On the other hand, communism promised economic and social equality, but the United States saw it as a threat to their values and system of government.
Furthermore, the victory of Communist forces in China and the outbreak of the Korean War intensified the fear of communism in the United States, as it seemed to validate their concerns about the spread of communism.