Solomon had challengers to the throne: Adonijah, just before David passed away (Not found elsewhere in the Bible). David’s fourth son was Adonijah, who was born after Absalom, who died earlier trying to take the throne (2 Samuel 15). Adonijah put himself forward as king, even though David had made it clear that Solomon would be king after him.
Adonijah waited as long as he could before he made his move. Yet he had to make his move before David passed, as was the custom and God-directed way. When David was getting so old that he could not care for himself (1-4), Adonijah made his move.
Adonijah did not have the backing of the high priest, the prophets, or the king’s professional soldiers and guards (10). This stands to reason because they were either loyal to God, David, or both. However, everyone else either backed him or did not challenge his attempt to seize the throne (9).
Nathan, the Lord’s prophet assigned to David, acted according to God’s direction and David’s wishes. He informed Bathsheba of Adonijah’s attempt to become king instead of Solomon, her son (11). Nathan gave sound instruction to her on how to stop it (12-14). Bathsheba agreed it was a sound plan and did as he instructed (15).
Obvious reasons exist why Adonijah wanted the seat of the highest power in the land. However, an even stronger reason existed. Verse 6 says, “His father had never interfered with him by asking, ‘Why do you behave as you do?'” David did not discipline Adonijah, nor did he instruct him in the way he should go. He did not punish him when he behaved civilly.
A wise father compliments and encourages his children. He does not exasperate them. Yet at the same time, a loving father teaches and punishes his children when they misbehave. Children need to learn social and family boundaries.

