1 Kings 15:30
Because of the sins of Jeroboam which he sinned, and which he made Israel sin, by his provocation wherewith he provoked the LORD God of Israel to anger. Because of the sins of Jeroboam which he sinned, and which he made Israel sin, by his provocation wherewith he provoked the LORD God of Israel to anger.
The verse gives the reason why Nadab son of Jeroboam was killed together with all of Jeroboam's kindred in the line of succession. Baasha carried out that killing after Nadab had reigned only a few months. In this the word of the Lord spoken by His servant Ahijah the Shilonite was fulfilled.
The cause was Jeroboam's sins — his own sin, his making Israel sin, and his provocation wherewith he provoked the Lord God of Israel to anger through the idolatrous worship he introduced. Thus the perishing of his house was Heaven's swift retributive judgment upon guilty offenders.