Complex sentence: With nuclear capabilities developed by the late 1950s, both the United States and the Soviet Union are poised as superpowers unprecedented in world history to each do massive devastation to the other or even totally annihilate their opponents.
Split into simpler sentences: With nuclear capabilities developed by the late 1950s, both the United States and the Soviet Union are poised as superpowers unprecedented in world history. Each has the ability to each do massive devastation to the other or even totally annihilate their opponents.