Final answer:
The correct answer is option (A) Warsaw Pact.
Step-by-step explanation:
In response to the founding of the North Atlantic Treaty Organization (NATO), Eastern European states organized a formal military alliance known as the Warsaw Pact. The Warsaw Pact was a military and political alliance that included the Soviet Union and the Communist nations of Eastern Europe, established in 1955 and lasting until the dissolution of the Soviet Union in 1991.
This alliance was formed as a counterbalance to NATO, particularly after West Germany joined NATO, signaling Western military and democratic consolidation against Soviet influence and Communist expansion.