What is the meaning of "Ga'arta Goyim"?
Radak: Ga'arah not followed by the prefix Beis is an expression of destruction, like "Ge'ar Chayas Kaneh" (68:31), "Hineni Go'er Lachem Es ha'Zera" (Mal'achi 2:3).
Which nations received Ga'arah?
Rashi: "Amalek Reishis Goyim" (Bamidbar 24:20).
Radak: The Pelishtim.
Malbim: Those who helped Laben.
Which Rasha did Hashem make perish?
Rashi: [Amalek's] fathers.
Radak: Galyus ha'Pelishti.
Malbim: Laben.
Whose name did He wipe out?
Rashi: Amalek - "Ki Macho Emcheh [Es Zecher Amalek]" (Shemos 17:14).
Radak: Those [Pelishtim] who died in the war.
Malbim: Laben and those who helped him. Once they started to fall in war, they did not rise. Afterwards, when they were in their houses, Hashem destroyed them.
