Rashi on Numbers 24:20/רש"י על במדבר כ״ד:כ׳

1וירא את עמלק AND HE SAW AMALEK — i.e. He perceived the retribution destined to befall Amalek.

2ראשית גוים עמלק AMALEK WAS THE BEGINNING OF NATIONS — he was the first of them all to war against Israel; thus, too, does Onkelos translate it. ואחריתו BUT HIS LATTER END will be to be destroyed by their hands, as it is said, (Deuteronomy 25:19) “Thou shalt blot out the memory of Amalek”.