Rashi on Numbers 33:40/רש"י על במדבר ל״ג:מ׳

1וישמע הכנעני AND THE CANAANITE HEARD This is stated here to tell you that Aaron’s death was indeed the news he heard — that the clouds of glory that until now had protected Israel had departed, and he therefore believed that liberty was now given to wage war against Israel. It is on this account that this is again recorded here (see Rashi on Numbers 21:1) (Rosh Hashanah 3a).