Amos was likely written in the mid 700 BC’s. Assyria was an aggressive nation and in the 800’s had asserted itself from its original territory (think parts of modern day Iraq and Iran) all the way over to the Mediterranean coast (modern day Israel-Palestine). However, by the 700’s, they had hit a lull and the two kingdoms of Israel (Israel and Judah) had experienced relative peace and earthly wealth/success. They believed God was providing this because He was pleased with them and awaited the day when God would bring justice upon the nations that surrounded them.
 
For a more extensive introduction, check out this video from the Bible Project: 
 

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