History
Understanding the Concept of Deterrence in International Relations
Quick fact
The key was 'mutual assured destruction': both sides knew that even a first strike would be met with a devastating counterattack, so starting a war would be suicidal. This created a 'balance of terror' that, ironically, prevented a full-scale war.
Why this is interesting
You've likely heard that the Cold War never turned into a direct war between the US and the Soviet Union. What stopped two superpowers with opposing ideologies from fighting on the battlefield?