Took the royal city. — The parallel narrative is resumed at this point in 1 Chronicles 20:2. Rabbah was situa…

And Joab fought against Rabbah of the children of Ammon
Of his being sent against it, and of his besieging it, we re…

To be this severe in putting the children of Ammon to slavery was a sign that David's heart was not yet softened by repentance, when this took plac…