The story of Israel directly post Joshua. And it is a story of incomplete conquering of the promised land.
For various reasons the people of God fail in their bravery and resolve. One tribe has iron chariots. Another is related to Moses. Some of the tribes, notably Benjamin who have Jerusalem, just don’t seem to try very hard.
What began as footnotes in Joshua becomes a river in judges 1, with a long list of areas of incomplete conquest at the end of chapter one.
I would probably have been among the incompletists. I reacted against god’s word that the existing people had to be defeated when I read Joshua. But I see the clarity of the principle of holiness.
They have integrated with the non believers in a similar way in which we allow sin to continue our lives and prevent the sanctification of ourselves by god’s spirit.
The rest of the book will, I gather, have a cyclic theme of faithlessness and return.