Jeroboam II was a king who did what was evil in the eyes of the Lord and led the people astray (2 Kings 14:24). He allowed for a powerful wealthy class to develop in Samaria (the capital of the northern kingdom). These people abused their wealth, power, and privilege and they are also the focus of Amos’s preaching.
The precise dates of Jeroboam’s reign as king of Judah are debatable. However, he likely ruled from 786-746 BC.
1 The words of Amos, who was among the shepherds of Tekoa, which he saw concerning Israel in the days of Uzziah king of Judah and in the days of Jeroboam the son of Joash, king of Israel, two years before the earthquake.