Many Christians don't know that Israel split into two kingdoms after the reign of king Solomon. For those who read the Bible, it's important to know about the split in order to have a better understanding of the Scriptures. The effects of the split had a large impact on the history of Israel, rippling even into the New Testament.
How It Happened
One of Solomon's servants, named Jeroboam, was on a road trip when he ran into a prophet named Ahijah, who predicted the split that was to come.
1 Kings 11:29-31
And at that time, when Jeroboam went out of Jerusalem, the prophet Ahijah the Shilonite found him on the road. Now Ahijah had dressed himself in a new garment, and the two of them were alone in the open country. Then Ahijah laid hold of the new garment that was on him, and tore it into twelve pieces. And he said to Jeroboam, “Take for yourself ten pieces, for thus says the Lord, the God of Israel, ‘Behold, I am about to tear the kingdom from the hand of Solomon and will give you ten tribes
However, it wasn't an arbitrary decision by God to divide the kingdom. It was idolatry that had provoked him:
1 Kings 11:33
because they have forsaken me and worshiped Ashtoreth the goddess of the Sidonians, Chemosh the god of Moab, and Milcom the god of the Ammonites, and they have not walked in my ways, doing what is right in my sight and keeping my statutes and my rules, as David his father did.
As you can imagine, Solomon wasn't to happy about the news of Jeroboam:
1 Kings 11:40
Solomon sought therefore to kill Jeroboam. But Jeroboam arose and fled into Egypt, to Shishak king of Egypt, and was in Egypt until the death of Solomon.
After Solomon died, the people came to his son, Rehoboam. They said his father had been too hard on them and hoped Rehoboam would make things a little easier. Rehoboam turned to his council for an answer. The old men said he should be easier on them but the young men said he should not. Rehoboam responded to the people:
1 Kings 12:11
“My father made your yoke heavy, but I will add to your yoke. My father disciplined you with whips, but I will discipline you with scorpions.”
Yeah, so that went over like a lead balloon and the 10 northern tribes seceded to form their own kingdom of which Jeroboam became king. The northern kingdom was referred to as Israel (sometimes Ephraim) and the southern kingdom was referred to as Judah (sometimes Jacob). The southern kingdom consisted of the tribes of Judah and Benjamin (and technically the tribe of Simeon, which was absorbed into Judah).
Many of the books of the Bible deal with the split kingdom and its ramifications. I speak in an episode of RE2 about the theme of brotherly reconciliation and how it may have been addressing the issues of a divided kingdom.