Another factor that is destabilizing and North Korea.
The story begins with the Civil War within Korea where Korea in 1950 divided into two parts: North Korea and South Koean.
It made a deal with the US to protect its border with the case of any attack South Korea and the US would respond militarily.
North Korea is to retaliate against the US and South Korea, by building nuclear missiles that threaten South Korea and UN response puts sanctions in order to disrupt financial resources.
But even this effort is not successful.