The book of Judges opens up with a little intro about precisely what work was left undone by the Joshua Generation. It specifically lists all of the indigenous people who were left within the Promised Land after the Israelite’s campaign.
In fact, after explaining that YHWH let the other people stay in the Promise Land as punishment for their disobedience, Jueces 2:1-4 (which I have to tell you feels suspicious to me because God’s angel doesn’t list any specific unpunished disobedience, but you know), we get this transition passage that alerts us to a new era:
After that whole generation had been gathered to their ancestors, another generation grew up who knew neither the Lord nor what he had done for Israel. Then the Israelites did evil in the eyes of the Lord and served the Baals. They forsook the Lord, the God of their ancestors, who had brought them out of Egypt. They followed and worshiped various gods of the peoples around them. They aroused the Lord’s anger
Jueces 2:10-12. The introduction closes noting the God did not abandon the people but instead would raise up judges from time to time to bring the people back to him. Those judges, spoiler alert, were only ever temporarily successful.
Interesting note: The NVI uses the term “caudillos” to describe the heroes described in this book in the intro, although notes that they are traditionally referred to a “jueces” and will use the term from here on out. According to google, caudillos = warlords. Jueces, of course, is judges. The NIV on the other hand points out that “leaders” may be a better translation, or at least an alternate.