Reading Judges 2:20-3:7
The cycle oft─repeated in Judges is the people are disobedient, God chastises them by oppressing enemies, they cry out to him, he raises up a Judge who delivers them, and then when the judge dies they revert to rebellion again.
God left pagan people in the land to test the resolve of his people (3:1-2, 4). Many became tributaries paying taxes or serving menial tasks. Methinks this is why we still have our old man or sinful flesh to fight against throughout our lives!
There followed seven years of war with Gilgal as the Israelite base in which they did not absolutely disable the Canaanites or take all their cities (Josh. 13:1, 13). Some of Judges 1 is recapitulation of Joshua 15:16-17 e.g., 1:8 and 12-13 and the rest describes the occupation of the land with individual tribes mostly fighting for their inheritance. Noteworthy that God directs proceedings in answer to prayer (1:2)–probably by High Priest’s Urim and Thummim.
Sadly the Israelites failed the test and intermarried with the pagans causing many to fall into idolatry (3:6)─this is almost inevitable if a believer marries an unbeliever (II Cor.6:14).