Final answer:
The Prague Spring was the seminal event that led to the collapse of the Soviet's hold on Eastern Europe.
Step-by-step explanation:
The seminal event that triggered the collapse of the Soviet's hold on Eastern Europe was the Prague Spring in which dissident Czechs challenged Gorbachev's rule. During this period in 1968, the Czechoslovak government aimed to implement political reforms that would grant more freedom to its citizens. However, the Soviet Union and other Warsaw Pact countries intervened militarily to suppress the movement and maintain their control over Eastern Europe.
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