Albert Barnes Commentary 2 Kings 11:17

"And Jehoiada made a covenant between Jehovah and the king and the people, that they should be Jehovah`s people; between the king also and the people." — 2 Kings 11:17 (ASV)

A covenant - Rather, “the covenant,” which either was already an established part of a coronation (see marginal reference “k”), or at least became so afterward.