(A) Soviet Union
(B) SATO
(C) ** Warsaw Pact
(D) Eastern Bloc
EXPLANATIONS BELOW
Concept note-1: -In May 1955 West Germany joined NATO, which prompted the Soviet Union to form the Warsaw Pact alliance in central and eastern Europe the same year.
Concept note-2: -In reaction to West Germany’s NATO accession, the Soviet Union and its Eastern European client states formed the Warsaw Pact in 1955. Europe settled into an uneasy stand-off, symbolised by the construction of the Berlin Wall in 1961.
Concept note-3: -The Soviet Union formed this alliance as a counterbalance to the North Atlantic Treaty Organization (NATO), a collective security alliance concluded between the United States, Canada and Western European nations in 1949. The Warsaw Pact supplemented existing agreements.
Concept note-4: -In the following 20 years, the Warsaw Pact countries outside the USSR each joined NATO (East Germany through its reunification with West Germany; and the Czech Republic and Slovakia as separate countries), as did the Baltic states which had been occupied by the Soviet Union.
Concept note-5: -The Warsaw Pact was created in reaction to the integration of West Germany into NATO in 1955 and represented a Soviet counterweight to NATO, composed of the Soviet Union and seven other Soviet satellite states in Central and Eastern Europe.