How Abusers Maintain Control Over Another Person

The three main methods Controllers keep control over a target is inducing fear of consequence for non-compliance to their commands and expectation; manipulation/lying; and lying and exaggerating to other people about a target.

People who aren't Controllers DON'T HAVE targets.
They don't trash others or participate in gossip about others.
They don't try to bully, dominate, and control others,
and they don't lie and omit information from the people in their lives who they're pretending to care about and be connected with in order to manipulate people and situations, or in order to make themselves look better. 
(with the exception of when they need to protect themselves or others from abuse).

This IS one of the reasons a Controller will target a specific person, because they don't fear CONSEQUENCES from the person.

They don't fear that the person will hit them back or threaten them back physically.
They don't fear that someone is going to stand up for them, especially when they have already slandered the target in order to convince people that he or she is a "bad person". (Since most modern humans seem to drink up back-stabbing others like good beer, it's easy for them.)
They don't fear that the person will retaliate somehow, because they know the person's VALUES and integrity are intact, and they just aren't going to do it.
They don't fear that the target is going to EXPOSE THEM, because again, they've already convinced people who the target would go to that the TARGET is a "bad person" and not to be trusted.

The overwhelming lack of maturity that plagues the human species is what allows Narcissism to persist. Most people don't stand up for others against even the smallest disrespects, never mind slander or abuse, generally. They are more likely to swallow gossip and slander hook, line, and sinker, quite willingly. And they are more likely to bully than to help a person who's already targeted; they're more likely to deny bully behavior (so they can keep doing it) than monitor their own behavior and motives, and they're more likely to ALLOW a target to be bullied and disrespected, instead of doing anything to stop it or even admit that it's happening.

Humans who don't stand up for others against disrespect, bullying, slander, or abuse are most likely ALSO DOING IT THEMSELVES, to someone else.