As noted in the introduction to the 1st book of Kings, both 1st and 2nd Kings in the Hebrew Old Testament are one book. That both books form one book is clear from the transition of 1 Kings to 2 Kings. 2 Kings begins with the mention of the death of Ahab. This is a continuation of the last chapter of 1 Kings (1Kgs 22:29-40). However, 1 Kings does not close with this. Following the mention of the death of Ahab, there is a short report of the kingship of Jehoshaphat over Judah, probably because of his relationship with Ahab and Ahab’s son. After that some more announcements are made about Ahaziah, who succeeds his father Ahab as king over Israel. That ends the first book of Kings.
A plausible reason for a separation in the histories in one great book of Kings may be that it would otherwise be too large a book. It is difficult to give a plausible reason for making that separation as it has been done. It has been suggested, a possible reason for why the separation was done that way, is to be similar to the one great book of Samuel. 2 Samuel begins with the mention of the death of Saul and 2 Kings begins with the mention of the death of Ahab.
The description of the course of history in 2 Kings is done in a way that is somewhat comparable to the way in which the writer presents the histories in 1 Kings to us. 1 Kings begins with the blessing and wisdom of Solomon and ends with the follies of the kings of the northern kingdom. The history of the ten tribes in the northern realm begins with Jeroboam, the ‘trendsetter’ for all the succeeding kings of that realm, and ends with Ahab, the king who completely apostatized from God.
The beginning of 2 Kings is essentially a record of the grace of God as presented through Elisha for an apostate nation. Despite this grace, the people slide completely away from God. 2 Kings ends with the exile of the ten tribes by the king of Assyria and the exile of the two tribes by the king of Babylon.