What caused the end of detente?

Answer 1

There were a lot of progressive reforms eyed in the USSR before it collapsed, detente and glasnost were some of the main ones. But when it did, a new government was elected and there was no need for gradual reform.

Answer 2

Either one side could gain from breaking the detente, or one side was attempting to mitigate the consequences of the other side breaking the detente first. Sometimes the breaking of the detente is mutual, as it is seen as inevitable. Sometimes some other influence forces the breaking of the detente. This can either be a single event or a long drawn out happening such as the increase of fear in the general populace such that they are provoked to demand action.

Answer 3

The Soviets invasion of Afghanistan.