‘ And Joshua smote them, from Kadesh-barnea, even to Gaza, and all the country of Goshen, even to Gibeon. And all these kings, and their land, did Joshua take at one time, because YHWH the God of Israel fought for Israel. And Joshua returned and all Israel with him to the camp at Gilgal.'
So after his victorious campaigns covering the whole of the south of Canaan Joshua returned with the army to their camp at Gilgal. Much had been done to prepare the way for conquest. But there had been no permanent occupation. That would follow later. ‘All Israel' returned to the camp at Gilgal. It would be up to the individual tribes finally to capture and occupy their own inheritance. He may well have thought that he had destroyed most of the opposition, but there would be many people still surviving his attacks, and outlying peoples would gladly move in to occupy vacant territory. There would still be much to do.
The account had a twofold purpose. It demonstrated that YHWH was able to give the whole country into their hands, and it showed that Israel later had no excuse for their failure to take full possession of it.
“From Kadesh-barnea even to Gaza.” This is describing the limits of the country dealt with. It does not necessarily signify that Gaza itself (on the coast) was taken. See Joshua 11:22. But the Philistines were probably not yet there, arriving later as their invasion of the territory also began (Joshua 13:2-3). Kadesh-barnea was an oasis in the Negeb on the edge of the wildernesses of Paran and Zin. The city of Goshen is mentioned in Joshua 15:51, the ‘country of Goshen' indicating widespread land connected with it. ‘Goshen to Gibeon' possibly indicated a recognised area in the highlands bounded by these two cities.