1 Kings 11:13

Howbeit, I will not rend away all the kingdom
The whole kingdom of Israel:

but will give one tribe to thy son;
but it seems he had both Benjamin and Judah, and only ten tribes were rent from him; the reason of this mode of expression may be, either because he gave him one of the tribes of Israel, besides that of Judah, which was his own tribe; or only the tribe of Judah is meant, the whole tribe of Benjamin not being his, since Bethel, and some other places in that tribe, were in the possession of Jeroboam; or rather both these are called but one, because their inheritances lay together, and were mixed with one another; and particularly both had a share in the city of Jerusalem, and the kingdom always after the division went by the name of Judah only: and this tribe was given

for David my servant's sake;
because of the promise to him, that there should not want one of his seed to sit on his throne, ( 1 Kings 9:5 )

and for Jerusalem's sake, whom I have chosen;
to have the house of his sanctuary and worship in, and therefore thought fit to have one rule there, that, would have a regard to his service in it.