40 years of King Solomon
The end of king Solomon's reign the Kingdom is split into two Kingdoms see Prophets and Divided Kingdom
He had only half a heart after God and is led away from God by his own actions.
Background Reading:
1st Kings 11:41-42
End of the 40 Year Reign of King Solomon and his death
41 As for the other events of Solomon's reign—all he did and the wisdom he displayed—are they not written in the book of the annals of Solomon? 42 Solomon reigned in Jerusalem over all Israel forty years. 43 Then he rested with his fathers and was buried in the city of David his father. And Rehoboam his son succeeded him as king.
also read 2 Chronicles 2:1-9:31