Numbers 21:1
And when king Arad the Canaanite, which dwelt in the south, heard tell that Israel came by the way of the spies; then he fought against Israel, and took some of them prisoners. And when king Arad the Canaanite, which dwelt in the south, heard tell that Israel came by the way of the spies; then he fought against Israel, and took some of them prisoners.
Arad was a Canaanite king who dwelt in the south, and he heard through spies that Israel was approaching near Mount Hor. Soon after Israel left Mount Hor, Arad attacked Israel with a large army, defeated them in battle, and took some Israelites prisoners.
Israel then besought the Lord to go with them to battle and to deliver the Canaanites into their hands, promising to utterly destroy their cities and to remain faithful in following God. In answer to earnest prayer the Lord heard them, went out with their armies, routed their enemies, and gave Israel victory so that they utterly destroyed them and their cities.
That victory over Arad and the Canaanites gave the surrounding nations further evidence that God was with Israel in His power and presence. Those nations could have been spared if they had not opposed God's word, but their refusal of the truth and continued idolatry brought them to the point of judgment. The victory should have led Israel to gratitude and dependence on God and tested whether they would trust Him in later difficulty, but instead they became boastful and self-confident, failed the test, and complained.