Israel defeated the Canaanite king of Arad and destroyed their cities.
Israel was refused passage through the land of Edom—Esau's descendants. So they turned southward towards the Red Sea and took the long route around Edom.
This path brought Israel into conflict with the Canaanite king of Arad.
1 Now the Canaanite king of Arad, who was dwelling in the desert, heard the news—for Israel came by way of Atharim—therefore, he made war against Israel; and they carried off captives from them as booty. 2 Then Israel made a vow to the Lord, and said, “If You will indeed deliver this people into my hand, I will anathematize him and his cities.” 3 So the Lord listened to the voice of Israel and delivered up the Canaanites; and they anathematized him and his cities. Therefore, they called the name of that place Anathema.
(Numbers 21:1-3 OSB)
The Canaanites secured the first victory, taking captives. This angered Israel and they called to GOD for help.
GOD gave them the victory and these cities and their citizens were wiped off the face of the earth.
We previously established how GOD gave Israel victory over the Amalekites (also descendents of Esau). With this additional conquest, the children of Israel should have been growing in confidence of GOD's ability and willingness to fulfill His promises to give them the land and conquer the Canaanites therein. Alas, these people were stubborn.