The children of Israel did that which was evil in the sight of Yahweh: and Yahweh delivered them into the hand of Midian seven years.
The Amalekites and other tribes that lived in the Arabian Desert east of Canaan joined the Midianites in their raids. These desert-dwellers were the "sons of the east" (Judges 6:3). The raids extended all the way to Gaza on the Mediterranean coast (Judges 6:4), far into Israel.