Final answer:
The scenario given exemplifies the security dilemma, a cycle where states' attempts to enhance security paradoxically lead to increased insecurity and tensions. This is distinct from concepts like Mutually Assured Destruction, which is about deterrence through the threat of mutually assured nuclear annihilation.
Step-by-step explanation:
The situation described in the question where two enemy nations each view the other's military buildup as a threat, despite their own similar actions, best illustrates the security dilemma. This dilemma occurs when a state's efforts to increase its security, such as through military buildups, makes other states feel less secure. It leads to a cycle where these states then also increase their military capabilities, which in turn makes the original state feel less secure, thereby escalating the situation between the two countries even further.
Mutually Assured Destruction (MAD) is a different concept, related to nuclear deterrence, where both sides possess nuclear capabilities sufficient to destroy the other, thus deterring them from initiating an attack.
Détente refers to a period of improved relations between superpowers, while Preemptive strike is a military attack launched with the intention of repelling or defeating a perceived imminent threat.