To actively demote someone to a lower position or rank.
When to use
Boss demotes subordinate, Manager lowers employee rank, Active action expression
The nuance
Used when the subject actively performs the act of demotion; an active verb.
강등하다 (gang-deung-ha-da, gangdeunghada) · 강등되다 (gang-deung-doe-da, gangdeungdoeda)
'강등하다' expresses the active act of demoting someone, while '강등되다' indicates being passively demoted.

One lane per word — no nested boxes, just the gist.
To actively demote someone to a lower position or rank.
When to use
Boss demotes subordinate, Manager lowers employee rank, Active action expression
The nuance
Used when the subject actively performs the act of demotion; an active verb.
To be demoted, indicating a passive state or situation where the subject is the receiver of demotion.
When to use
Employee is demoted, Player's rank is lowered, Passive state expression
The nuance
Used when the subject is the receiver of demotion, expressing a passive state.
사장은 직원을 강등했다.
sa-jang-eun jik-won-eul gang-deung-haess-da., sa jang eun jik won eul gang deung haess da.
The subject (boss) actively performed the action, so active verb '강등하다' is correct.
사장은 직원이 강등되었다.
sa-jang-eun jik-won-i gang-deung-doe-eoss-da., sa jang eun jik won i gang deung doe eoss da.
The subject and verb's agent mismatch; correct would be '직원이 강등되었다'.
그는 강등되었다.
geu-neun gang-deung-doe-eoss-da., geu neun gang deung doe eoss da.
The subject is the receiver of demotion, so passive '강등되다' is correct.
그는 강등했다.
geu-neun gang-deung-haess-da., geu neun gang deung haess da.
The subject is not actively demoting anyone, so active '강등하다' is incorrect.
회사는 문제 있는 직원을 강등했다.
hoe-sa-neun mun-je iss-neun jik-won-eul gang-deung-haess-da., hoe sa neun mun je iss neun jik won eul gang deung haess da.
The subject actively performs demotion, so '강등하다' is correct.
문제 있는 직원이 강등되었다.
mun-je iss-neun jik-won-i gang-deung-doe-eoss-da., mun je iss neun jik won i gang deung doe eoss da.
The subject receives demotion, so passive '강등되다' is correct.
회사는 강등되었다.
hoe-sa-neun gang-deung-doe-eoss-da., hoe sa neun gang deung doe eoss da.
Companies usually do not get demoted; passive form here is unnatural.
직원은 상사에게 강등되었다.
jik-won-eun sang-sa-e-ge gang-deung-doe-eoss-da., jik won eun sang sa e ge gang deung doe eoss da.
Subject is passively demoted, so passive '강등되다' is correct.
Which word to use when actively demoting someone?
Which word to use when you are passively demoted?
In 'The company ___ the employee', which word fits?