Strictly speaking, they didn’t have to, for Jerusalem lay just inside the boundary of Benjamin (Joshua 18:16, Joshua 18:28). But this powerful city would pose a threat to the men of Judah and Simeon for as long as it remained in enemy hands; so it had to be captured swiftly. God gave it into their hands. They left, giving the task to Benjamin to keep the city under Israel’s control. Judges 1:21 reveals, however, that the Jebusites filtered back in and took control again.1
8 And the men of Judah fought against Jerusalem and captured it and struck it with the edge of the sword and set the city on fire.