The children of Israel again did that which was evil in the sight of Yahweh, and served the Baals, and the Ashtaroth, and the gods of Syria, and the gods of Sidon, and the gods of Moab, and the gods of the children of Ammon, and the gods of the Philistines; and they forsook Yahweh, and didn't serve him.
The text reveals that the Philistines and the Ammonites began to oppress Israel simultaneously from the west and the east respectively. The writer proceeded to narrate the Ammonite account first (Judges 10:8 to Judges 12:7) and then the Philistine (Judges 13:1 to Judges 16:31).