Aperson who intentionally tries to drive a wedge between two other people is termed by georg simmel as:

I believe the answer is: divide and conquer

divide and conquer is usually being carried out by influencing local leaders to rebel and challenge the power of main authority.
By doing this, the people that initiate divide and conquer could be diminished a kinngdom/organization power without having to make sacrifices.

Low risk and moderate growth.

Yes, they are always very triggered