This is a great question and the way you ask it shows that you know the dominant pattern or cycle in the book of Judges. There is a cycle that repeats itself several times and the question that the book does not resolve is: "Who will deliver the Israelites from this cycle of sin?" We see this is the bulk of the book. Here is a brief outline:
1. Incomplete Conquest 1:1-2:5 2
2. The Pattern of Disobedience 2:6-3:6
3. The Pattern Illustrated: A history of the Judges 3:7-16:31
After chapter 17, there is a total spiraling down of Israel.
What you need to focus on is Judges 2:6 - 3:6. In this section, we see the five "R's." The people rebel against God. In other words, they forget him and follow after false gods. After this they are rebuked usually by an enemy that subdues them. At this point the Israelites repent and turn back to God. God hears them and raises up a judge to resuce them. Finally, there is rest in the land. After a while, the Israelites forget about God and rebel again and the cycle starts anew.