Albert Barnes Commentary 2 Samuel 19:8

"Then the king arose, and sat in the gate. And they told unto all the people, saying, Behold, the king is sitting in the gate: and all the people came before the king. Now Israel had fled every man to his tent." — 2 Samuel 19:8 (ASV)

David saw the justice of what Joab said and the new danger which threatened him if he did not rouse himself from his grief.

For Israel refers not to David’s followers, but to Absalom’s army, as in 2 Samuel 17:26; 18:6; and 18:17.