Answer
There are two kings with the name Joash (or Jehoash) in the Bible: one a king of Judah (reigned 835–796 BC) and the other a king of Israel (reigned 798–782 BC).
The story of King Joash of Judah starts with that of King Jehu of Israel. Anointed king of Israel by Elisha, Jehu was tasked with destroying King Ahab’s descendants and wiping out Baal worship in the land (2 Kings 9). First Kings 21:25–26 gives the reason for the judgment: “There was never anyone like Ahab, who sold himself to do evil in the eyes of the Lord, urged on by Jezebel his wife. He behaved in the vilest manner by going after idols, like the Amorites the Lord drove out before Israel.” God had told Ahab, through Elijah, “I am going to bring disaster on you. I will wipe out your descendants and cut off from Ahab every last male in Israel—slave or free, . . . because you have aroused my anger and have caused Israel to sin” (1 Kings 21:21–22). Ahab responded to the prophecy with mourning and in humility, so God relented, saying that He would not bring the disaster in Ahab’s time but during his son’s reign. Jehu was God’s instrument to fulfill the prophecy.
After Jehu was anointed king over Israel, he set out against Joram, a son of Ahab and the current king of Israel. Ahaziah (different from the other son of Ahab who initially succeeded him) was king of Judah at the time and was with Joram. Judah’s Ahaziah, however, “followed the ways of the house of Ahab and did evil in the eyes of the Lord, as the house of Ahab had done, for he was related by marriage to Ahab’s family” (2 Kings 8:27). Jehu killed both Ahaziah and Joram; executed Ahab’s wife, Jezebel; killed Ahab’s descendants; and “wiped out Baal from Israel” (2 Kings 10:28, ESV). Unfortunately, Jehu himself did not walk in the ways of God, but, since he had been faithful to God’s call to rid Israel of Baal worship, God promised that four generations of his line would be king of Israel (2 Kings 10:30).
King Joash of Judah first comes on the scene when Athaliah, the mother of King Ahaziah, whom Jehu had killed, took charge of Judah. Athaliah killed all of the royal family she could find in Judah in order to secure the throne for herself. However, Athaliah missed one of her grandsons—the infant Joash. The evil queen’s daughter (or possibly step-daughter) rescued young Joash and his nurse, and the child was hidden for six years in the temple while Athaliah reigned in Judah (2 Kings 11:1–3). In the seventh year, the priest Jehoiada revealed Joash to the captains of the guards. The priest made an agreement with them to provide protection to the temple and the rightful king, and Jehoiada brought Joash out into public and anointed him as king (2 Kings 11:4–12). The people of Judah rejoiced over Joash’s appointment. Upon hearing the noise of the ceremony, Queen Athaliah rushed to the temple, crying, "Treason! Treason!” By Jehoiada’s command, Athaliah was captured by the guards, removed from the temple, and put to death (2 Kings 11:13–16). “Jehoiada then made a covenant between the Lord and the king and people that they would be the Lord’s people. He also made a covenant between the king and the people” (2 Kings 11:17). The people tore down the temple of Baal, watchmen were set over the Lord’s temple, and, at the age of seven, Joash took the throne (2 Kings 11:18–21).
Second Kings 12:1–3 says that Joash “reigned in Jerusalem forty years. . . . Joash did what was right in the eyes of the Lord all the years Jehoiada the priest instructed him.” Second Kings 12 goes on to describe various financial dealings of Joash. King Joash’s main achievement was making repairs to the temple (2 Kings 12:4–16). He also used a monetary gift to dissuade King Hazael of Aram (Syria) from attacking Jerusalem (2 Kings 12:17–18).
The tragedy of King Joash of Judah is that, after his mentor and guardian, Jehoiada, died, he began listening to wicked advisers. Joash revived Baal and Asherah worship in Judah (2 Chronicles 24:17–19). God sent prophets to warn Joash, but he did not listen to them. Finally, the prophet Zechariah, son of the priest Jehoiada, brought God’s word to Joash, but the king callously ordered the son of his old friend to be stoned to death (verses 19–22). Joash’s reign did not end peacefully: “His officials conspired against him and assassinated him at Beth Millo, on the road down to Silla” (2 Kings 12:20). Joash’s son Amaziah took over the throne, and Amaziah “did what was right in the eyes of the Lord,” but, the Bible notes, he was more like his father Joash than his ancestor David (2 Kings 14:3–4). Interestingly, Amaziah interacted with the other King Joash in the Bible.
King Joash of Israel began his reign in the thirty-seventh year of the reign of King Joash of Judah, so there was some overlap. King Amaziah started ruling Judah in the second year of King Joash of Israel. Amaziah of Judah battled against the Edomites and then challenged Joash of Israel to battle (2 Kings 14:7–8). Joash refused, essentially telling Amaziah he was needlessly stirring up trouble (2 Kings 14:9–10). Amaziah did not heed the warning, and Joash of Israel defeated Judah in battle. Second Chronicles 25:20 says that Judah’s defeat was “because they sought the gods of Edom.”
Second Kings records another of Joash of Israel’s military victories. When Joash’s father, Jehoahaz, was reigning, King Hazael of Aram (the same king that Joash of Judah had kept from attacking Jerusalem) oppressed Israel (2 Kings 13:22). “But the Lord was gracious to them and had compassion and showed concern for them because of his covenant with Abraham, Isaac and Jacob. To this day he has been unwilling to destroy them or banish them from his presence” (2 Kings 13:23). When the prophet Elisha was sick and near to death, King Joash of Israel visited the prophet, apparently disconcerted over the military situation in Israel (2 Kings 13:14). Elisha instructed Joash to shoot arrows out of the open window. The prophet then proclaimed, “The Lord’s arrow of victory, the arrow of victory over Aram! . . . You will completely destroy the Arameans at Aphek” (2 Kings 13:17). Elisha next instructed Joash to strike the ground with the arrows. Joash did so but stopped after three strikes. “The man of God was angry with him and said, ‘You should have struck the ground five or six times; then you would have defeated Aram and completely destroyed it. But now you will defeat it only three times’” (2 Kings 13:19). When Hazael died and his son, Ben-hadad, took over, Joash did defeat him three times. Israel was able to recover cities that previously had been taken from them (2 Kings 13:24–25).
King Joash of Israel ruled for sixteen years and “did evil in the eyes of the Lord and did not turn away from any of the sins of Jeroboam son of Nebat, which he had caused Israel to commit; he continued in them” (2 Kings 13:11). After he died, Joash of Israel was succeeded by his son Jeroboam II (2 Kings 14:16).