It should seem that, as this verse is inclosed in a parenthesis, it only meant to notice what had been said before. Probably Jerusalem was taken in the wars of Joshua. See Joshua 10:1, etc.
Judges 1:3-8
3 And Judah said unto Simeon his brother, Come up with me into my lot, that we may fight against the Canaanites; and I likewise will go with thee into thy lot. So Simeon went with him.
4 And Judah went up; and the LORD delivered the Canaanites and the Perizzites into their hand: and they slew of them in Bezek ten thousand men.
5 And they found Adonibezek in Bezek: and they fought against him, and they slew the Canaanites and the Perizzites.
6 But Adonibezek fled; and they pursued after him, and caught him, and cut off his thumbs and his great toes.
7 And Adonibezek said, Threescore and ten kings, having their thumbsa and their great toes cut off, gathered their meat under my table: as I have done, so God hath requited me. And they brought him to Jerusalem, and there he died.
8 Now the children of Judah had fought against Jerusalem, and had taken it, and smitten it with the edge of the sword, and set the city on fire.