Most Bible students will know that Israel’s first three kings were Saul, David, and Solomon. They were the only three kings to rule over all twelve tribes, what scholars call the united monarchy. The complete kingdom was known in the Old Testament as Israel, since the twelve tribes of Israel swore allegiance to the same king. Solomon’s reign ends in 1 Kings 11. That means the united monarchy—the lives of Saul, David, and Solomon—are covered in 1–2 Samuel and 1 Kings 1–10.
After Solomon died, ten of the tribes seceded from the nation and formed their own kingdom. From that point on, the way biblical writers referred to both political entities can be confusing.
The two tribes left after the secession were Judah and Benjamin. The latter was a tiny tribe and geographical area. Judah was much larger and the place where Jerusalem, the former capital of the united monarchy, was located. Judah was the tribe of David, whom God had chosen and whose lineage God had declared by a covenant was the only legitimate dynasty for rule over his people (2 Sam. 7). Both Judah and Benjamin were located in the southern section of the promised land. As a result, the southern kingdom of these two tribes became known as Judah.
The ten tribes who had defected from David’s dynasty were a different story. Since they comprised the bulk of the land and the tribes, they retained the name “Israel” as a political entity. That means that, after the kingdom split in 1 Kings 11, “Israel” often refers only to the ten tribes. Most of the territory covered by these ten tribes covered the northern part of the promised land, and so this “Israel” is also referred to as the northern kingdom.
To make things more complicated, the ten-tribe nation of “Israel” also went by other names. The central hill country of the land was dominated by the territory of the tribe of Ephraim. Jereboam, the first king of the renegade ten tribes, built his capital (Shechem) in Ephraim. However, Ephraim’s own capital had been Samaria. After the time of Jereboam, Samaria became the capital of the northern kingdom. Consequently, the ten-tribe northern kingdom of “Israel” was also known as Ephraim and Samaria.
All of this has an impact on our reading of the Old Testament’s historical material after 1 Kings 11, as well as books of the prophets who lived after the original kingdom split. “Israel” in those books mostly refers to only ten tribes and is interchangeable with Ephraim and Samaria.