2 Chronicles 21:4

4 And Jehoram rose up on the realm of his father; and when he had confirmed himself in the realm, he slew all his brethren by sword, and also some of the princes of Judah. (And when Jehoram had taken his father's kingdom, and established himself on the throne, he killed all of his brothers by the sword, and also some of the leaders of Israel.)

2 Chronicles 21:4 Meaning and Commentary

2 Chronicles 21:4

Now when Jehoram was risen up to the kingdom of his father,
&c.] Succeeded him in it, and reigned alone, for he had reigned with his father some years before his death; (See Gill on 2 Kings 8:16), he strengthened himself;
in the kingdom, by some means or another closely attaching the greater part of the princes, and people of the land, unto him, when he thought himself well settled and established on the throne; though some understand it of making strong, or hardening his heart to do what is next mentioned: and slew all his brethren with the sword;
either to get their riches into his hands, or lest, being religious princes, they should oppose his restoring idolatry, and for that reason the people should depose him, and set up one of them; and therefore he dispatched them out of the way to secure himself, and carry his point: and [divers] also of the princes of Israel;
such who had removed out of the ten tribes, for the sake of religion, and therefore would never agree to the introduction of idolatry among them, for which reason Jehoram slew them; and perhaps they might express their disapprobation and abhorrence of his murder of his brethren.

2 Chronicles 21:4 In-Context

2 And he had brethren, the sons of Jehoshaphat, Azariah, Jehiel, and Zechariah, and (another) Azariah, and Michael, and Shephatiah; all these were the sons of Jehoshaphat, king of Judah.

3 And their father gave to them many gifts of gold and of silver, and he gave them pensions, or rents, with full strong cities in Judah; but he gave the realm to Jehoram, for he was his first begotten son. (And their father gave them many gifts of gold and of silver, and he gave them pensions, or rents, along with fortified cities in Judah; but he gave the kingdom to Jehoram, for he was his first-born son.)

4 And Jehoram rose up on the realm of his father; and when he had confirmed himself in the realm, he slew all his brethren by sword, and also some of the princes of Judah. (And when Jehoram had taken his father's kingdom, and established himself on the throne, he killed all of his brothers by the sword, and also some of the leaders of Israel.)

5 Jehoram was of two and thirty years, when he began to reign; and he reigned eight years in Jerusalem.

6 And he went in the ways of the kings of Israel, as the house of Ahab had done, for the daughter of Ahab was his wife; and he did evil in the sight of the Lord.