Charles Ellicott Commentary 1 Chronicles 19:15

"And when the children of Ammon saw that the Syrians were fled, they likewise fled before Abishai his brother, and entered into the city. Then Joab came to Jerusalem." — 1 Chronicles 19:15 (ASV)

And when the children of Ammon saw. — The Hebrew construction is quite different from that of 1 Chronicles 19:6. Render, Now the sons of Ammon had seen that Aram was routed.

They likewise. — An explanatory addition to the text, as read in Samuel. So also “his brother.”

Then Joab came ... — Abridged. (Compare Samuel.)