Final answer:
The correct answer is option 4. The military alliance formed by the USSR with Eastern European communist countries is known as the Warsaw Pact, established in response to NATO's inclusion of West Germany in 1955.
Step-by-step explanation:
The military alliance formed by the USSR with other communist countries in Eastern Europe is known as the Warsaw Pact. This pact was created as a direct response to the formation of NATO by Western nations. In May 1955, following West Germany's integration into NATO, the Soviet Union sought to strengthen its own military and political stance by convening a meeting in Poland that led to the formation of the Warsaw Pact.
The pact included nations such as Albania, Bulgaria, Czechoslovakia, Hungary, Poland, Romania, and the German Democratic Republic (East Germany). Its establishment was a significant move in the context of the Cold War, marking the division of Europe into the Eastern Bloc under the influence of the Soviet Union and the Western Bloc under the influence of the United States and its allies. The Warsaw Pact remained active until the dissolution of the Soviet Union in 1991.