Question

What accounts for why the Soviet Union decided to formalize its East European alliance through the Warsaw Pact

Answer 1

Well, according the Soviets, the formation of the North Atlantic Treaty Alliance (NATO) and in particular the inclusion of West Germany into it. The Soviets felt that allowing Germany, the recent enemy, to join NATO -- and only part of it at that, the part under Western occupation -- was a provocative move.

Who knows? They probably did feel threatened. Cold War tensions were very high in the mid 1950s, and the Soviet Union was in some turmoil trying to reorganize after Stalin's death in 1953. Furthermore, the American President, Dwight Eisenhower, was a canny and effective cold warrier, who by various means some public and some secret routinely kept the Soviets anxious and fearful.