As soon as his kingdom was established, Amaziah executed the murderers of his father, but he permitted their children to live[4] in obedience to the Mosaic law: According to Chronicles, Amaziah was the first to employ a mercenary army of 100,000 soldiers from Efraim (a force significantly larger than the one Alexander used for his conquest of Asia-minor) with 100 talents, as a supplement to his 300.000 Judean soldiers, in an attempt to reconquer Edom, which had rebelled during the reign of Jehoram, his great-grandfather.

Due to the Israelite mercenaries' anger at being excluded from the battle, they attacked and looted multiple towns in Judah.

To compass his chastisement, God inspired Amaziah with the idea of provoking a war with Joash, the ruler of the northern kingdom.

Amaziah demanded that Joash should either recognize the suzerainty of the southern realm voluntary, or let the fate of battle decide the question.

At first Jehoash sought to turn Amaziah aside from his purpose by a parable reminding him of the fate of Shechem, which the sons of Jacob had visited upon him for having done violence to their sister Dinah.

The king was captured, 400 cubits of the wall of Jerusalem was broken down, the city, Temple, and palace were looted, and hostages were carried to Samaria.

[4] Amaziah was killed by his own subjects at Lachish, to which he had fled, and his body was brought to Jerusalem, where it was buried in the royal sepulcher (2 Kings 14:19–20; 2 Chronicles 25:27–28).