Why does it say "Al ha'Yom ha'Ba"?
Malbim: This refers to verse 2 - "Ko Amar Hashem
Why does it mention "Tzur" and "Tzidon"?
Rashi: Pelishtim used to help them against their enemies. Radak - they are from the region of Pelishtim - "Tzur v'Tzidon v'Chol Gelilos Pelashes" (Yo'el 4:4).
What is "Iy Kaftor"?
Rashi: It is the island of Kaftor.
Why does it mention "Kaftor"?
Radak, Malbim: Pelishtim and Kaftorim are brothers - "Asher Yatz'u mi'Sham Pelishtim v'Es Kaftorim" (Bereishis 10:14).
Will there be a remnant from Pelishtim?
Radak: No. Malbim (1, 4) - this is because (a) the Pelishtim helped Tzur and those with whom [Tzur] had a covenant. Nebuchadnetzar warred with Tzur and their Ba'alei Bris; he will wipe out those who helped them, so they will not have help. (b) It was Hashgachah from Hashem.