John Gill Commentary 2 Samuel 18:16

"And Joab blew the trumpet, and the people returned from pursuing after Israel; for Joab held back the people." — 2 Samuel 18:16 (ASV)

And Joab blew the trumpet
As the sign of a retreat:

and the people returned from pursuing after Israel ;
upon the sound of the trumpet, the meaning of which they understood:

for Joab held back the people :
from shedding any more blood; the head of the conspiracy being removed, the thing would be crushed at once; and Joab neither chose to slay any more, nor take any prisoners, to be tried as traitors, being unawares, without thought, drawn into this rebellion.