Thematic Bible: Intermarrying with, of kings considered treason

And she said, Let Abishag the Shunammite be given to Adonijah thy brother to wife. And king Solomon answered and said unto his mother, And why dost thou ask Abishag the Shunammite for Adonijah? ask for him the kingdom also; for he is mine elder brother; even for him, and for Abiathar the priest, and for Joab the son of Zeruiah. Then king Solomon sware by Jehovah, saying, God do so to me, and more also, if Adonijah hath not spoken this word against his own life. read more.
Now therefore as Jehovah liveth, who hath established me, and set me on the throne of David my father, and who hath made me a house, as he promised, surely Adonijah shall be put to death this day.