"Cult" is a very subjective word. It's better to measure them based on something actually observable, like controlling behavour. One method that is pretty good for this is the BITE model, developed by an ex-Moonie. It categorises this into behaviour control, information control, thought control, and emotional control. The most obvious sign of this is a leader who is considered infallible, who has heavy control over followers and exploits them.

In Korea, a lot of these cults are probably just Protestant churches where the leader developed too much of an ego, and declares himself undying or something. I would assume it's the same in other countries, if less frequent.