If you read all of Judges 1 you will see that many tribes who had the LORD with them failed to remove their enemies. All this simply means is that the Israelites chose to rely on their own powers instead of God and we're defeated in every way. Had they relied on their God they would have accomplished all they had set out to do. Later we find that God admonishes them for not doing what they were instructed to do and for centuries to come, the pagans would be a thorn in the side of the Israelites.
