Amos
Amos was mostly upset with how people in the northern kingdom were treating each other. The rich were nasty to the poor, and Amos said that they would suffer for it. Some of them thought that they could offer sacrifices (their equivalent of our “going to church”) and be ok with God. Amos told them they were wrong. Still, even with all of Amos’s warnings about judgments, he ends his book with a very amazing promise of God’s blessing for the future.
Obadiah
Why does Edom get a whole book devoted to its sin and destruction? First, because of all nations, they should have treated Israel better because they are “brother” countries (Jacob/Israel and Esau were brothers). Second, because in Scripture, Edom often stands for any nation that would hurt Israel (and thus stand against God’s purposes).