Final answer:
McCarthyism was driven by the Cold War, fears of the Soviet Union, and a political agenda prioritizing the containment of Communism. Internal context played a role but was intertwined with and overshadowed by international pressures and events. McCarthy used fear and unsubstantiated allegations for political gain within this broader context.
Step-by-step explanation:
The main reason for McCarthyism did not lie solely within internal context. McCarthyism was largely fueled by the geopolitical tensions of the Cold War, the suspicion against the Soviet Union, and the widespread fear of Communism. Internal factors did contribute to the hysteria; however, they were magnified and exacerbated by the larger international context. This period was marked by a political agenda that often sacrificed individual rights in the name of national security, and political leaders didn't want to appear soft on Communism. As the Cold War tensions heightened, Americans were less taken in by demagogues like McCarthy who leveraged fear for their own political advancement.
McCarthy, in particular, capitalized on this fear by using unsubstantiated allegations which resonated with the public and fellow politicians who were equally afraid of being labeled soft on Communism. As part of the United States' attempts to present a strong front against Communism internationally, this domestic policy of rooting out alleged Communists was also influenced by the international objective of containing Communism. This objective became a priority after events such as the Communist victory in China and the Korean War, further underscoring that internal policies were closely tied to international concerns.