Judges 2:11

And the children of Israel did evil in the sight of the LORD, and served Baalim:

The verse describes a new generation that arose after Joshua died, turning from the Lord to worship Baalim. Their fall came after Joshua and the elders who outlived him died and their steadfast reproof and warning ceased. Before this, Israel had served the Lord all the days of Joshua in a genuine revival and reformation marked by true contrition, confession, and forgiven sin, yet the seed of evil had been sown.

Their evil followed their failure to know the Lord and remember His works, including bringing Israel out of Egypt. The seed of evil sprang up to bear fruit in a people whose worship was mingled with erroneous principles and ambitious pride. Doing evil meant forsaking the Lord God of their fathers, departing from allegiance to God in apostasy. Serving Baalim meant worshiping, following, and bowing to the gods of the surrounding peoples, the gods of the peoples round about them.

This idolatry provoked the Lord to anger. In hot anger for their transgression of His covenant and disobedience to His voice, He would no longer drive out the nations Joshua left but would leave them to prove whether Israel would keep the way of the Lord or not. This disloyalty, this departing from allegiance to God, brought disaster and defeat upon them.