Answer:
The Cold War between the United States and the Soviet Union.
Explanation:
The Cold War presented an interesting situation for researches in game theory. This is because in the Cold War, two superpowers were fighting, or "gaming" for supremacy in the world state, and as a result, they were two players more or less matched in capacity.
Besides, because both countries had nuclear weapons, they had a quality known as mutual assured destruction, which means that if either one or the two ever used the nuclear weapons, the two countries would essentially self-destroy.
For this reason, strategy was of greatest importance for both superpowers, and finding the best strategy to be victorious was the main focus of the game theory researches, and what led to the boom in game theory research in recent decades.