In one way or another, these Gentile nations took vengeance in retaliation for injustices that they believed other nations committed against them. God promises to judge their barbarity, but He does not say when. Many years may pass before He takes action because His overriding goal is repentance and a change in character.
He will execute proper judgment—true justice, and it is our responsibility to have faith in that. Fifty years passed before God avenged the depredating acts of Hazael, king of Syria, against Gilead (Amos 1:3; II Kings 10:32-33). God waited for the right time and place to act. But He did act with a punishment from which He will not turn back (II Kings 13:22-25). When He decides to act, He acts!
When He says that He knows our sitting down and rising up (Psalm 139:2), He is not speaking metaphorically. He is involved with His people. We must learn that sometimes God may not take action within our lifetime, but when He says, "I will repay" (Romans 12:19; Deuteronomy 32:35), He means it!
John W. Ritenbaugh
Prepare to Meet Your God! (The Book of Amos) (Part One)