Here we are given a summary of what we are going to see in the rest of the book of Judges. Since the Canaanites were not eliminated, generations of people who came after Joshua were deceived into following false gods. As a result, God could no longer give them success. Baal refers to a specific false god and also generically to false gods. Ashtareth was a false goddess. Baal was considered to be the god of storms or rain. Since the success of the people was extremely dependent on rain, it was tempting to worship this god. It was believed that it rained when Baal and Ashtareth had sex, so the worship of Baal included prostitution to remind Baal of what they wanted him to do. This also made the worship of Baal tempting. God raises up deliverers for Israel called judges. Generally, these are people who lead the people militarily and spiritually, but their positive influence never becomes permanent.
Incomplete obedience leads to greater disobedience, not greater obedience. It takes intervention to move in the right direction.