Meaning of “break down” - Learner’s Dictionary

break down

phrasal verb with break uk us /breɪk/ verb (past tense broke, past participle broken)
MACHINE

B1 If a machine or vehicle breaks down, it stops working:

My car broke down on the way to work.
COMMUNICATION

If a system, relationship, or discussion breaks down, it fails because there is a problem or disagreement:

Their marriage broke down after only two years.
CRY

to become very upset and start crying

(Definition of “break down” from the Cambridge Learner’s Dictionary © Cambridge University Press)