To come about is to happen, and it is used most in asking how something started. How did that come about, it will come about slowly.
It nearly always follows how, which is the shape most people meet it in. In sailing it has a separate sense of turning a boat through the wind.
1phrasecome aboutTo happen — used when asking how something started.
“Nobody could say how the arrangement had come about.”
come about is a phrase.
Practised in Phrasal Verbs