Able Archer 83

Able Archer 83 was a military exercise (a game) that NATO (an alliance of many countries) played in the 1980s. It was a game to practice how to defend against a real attack, like a war. The game was meant to be a war-game, but the Soviet Union (a former country in Europe) thought it was a real attack and got scared. They thought the real war was actually happening. Some people even thought that there was going to be a real war. Luckily, it was all just pretend and no real war happened.