Commentary for Amos 1:8

1: and therefore the nation that dwells in Ashdod will be destoryed and the rulership will be removed from Ashkelon. They they are all Philistine cities, Aza, Ashdod and Ashkelon and Akron. Gath is not mentioned here because it was a city of the the kingdom of Judah. And when the prophet says "I will destroy the remnant of the Philistines" you will see the truth of what I said because the prophecy of Amos came after the prophecy of Yoel, chronologically. And because Amos heard Yoel's prophecy about the destruction of Tzur and Sidon and the districts of the Philistines therefore Amos prophecy dealt with the other Philistine cities and that's what was mean by the "remnants of the Philistines."

Ashdod... Ashkelon... Ekron—They were the lords of the Philistines.

and I will return My hand—I will smite them repeatedly.