Shared ground
These verses describe a quick shift in a two-front battle. Joab advances against the Arameans, and they flee. The Ammonites notice their allies have broken and, rather than fight on their own, they also flee from Abishai and pull back behind city walls. Joab then returns to Jerusalem, marking the end of this immediate engagement.
The text’s emphasis is on momentum and perception: one side’s retreat changes the other side’s calculation. It also highlights coordinated Israelite leadership (Joab and Abishai) and the tactical importance of fortified cities once an open-field position fails.
Where interpretation differs
Some readers take “they fled” as a full collapse (a rout). Others think it could be a more controlled withdrawal, since the passage does not describe pursuit, casualties, or capture.
Some also differ on how to read Joab’s return to Jerusalem: either as a strategic pause after pushing the enemy back into a city, or as evidence that the battle achieved only a limited outcome without immediately transitioning into a siege.
Why the disagreement exists
The passage reports outcomes but leaves details unstated. It does not explain how far the flight went, whether Israel pursued, exactly which “city” is meant, or why Joab chose to disengage rather than press the advantage.
What this passage clearly contributes
Explicitly, it shows (1) Joab’s forward movement leads to Aramean retreat, (2) Ammon’s retreat is triggered by seeing that retreat, (3) the fight shifts from open field to a fortified-city situation, and (4) the narrative pauses with Joab back in Jerusalem (cf. the close parallel in 2 Samuel 10:13–10:14). Theologically by inference (not stated directly), it portrays conflict outcomes turning on leadership, morale, and the strategic refuge that city walls provide, while keeping the focus on the immediate result rather than extended battle description.