Definition of intervenes:
(v) :
(intransitive) To become involved in a situation, so as to alter or prevent an action. [with in]
(v) :
(ambitransitive) To say (something) in the middle of a conversation or discussion between other people, or to respond to a situation involving other people.
(v) :
(ambitransitive) To come between, or to be between, persons or things.
(v) :
(intransitive) To occur, fall, or come between, points of time, or events.
(v) :
(intransitive) To occur or act as an obstacle or delay.
(v) :
(law) In a suit to which one has not been made a party, to put forward a defense of one's interest in the subject matter.