Ahijah's Prophecy
From the days when Israel demanded a king like the other nations, not recognising that Yahweh was their king, Israel had been heading toward conflict. 2 Samuel 20 With the increase of Idolatry in Israel through Solomon's wives, God purposed to divide the kingdom in two in order to preserve for himself a people who would be faithful. God sends Ahijah the prophet out into a field wearing a new garment. When he finds Jeroboam he takes and rips his new garment into twelve pieces and gives ten of them to Jeroboam. This symbolic gesture indicates that ten of the tribes would be torn out of Solomon's hands and given to Jeroboam. 1 Kings 11:29-31
Ahijah also makes a prophecy that God would make a great nation out of Jeroboam's descendants. This prophecy did not make the Davidic covenant null and void, but it does offer a similar promise of blessing to the nation of Israel conditioned on obedience. 1 Kings 11:38
Division of the Kingdom
The Kingdom was broken up into two nations, Israel in the North and Judah in the south. The Northern kingdom consisted of the majority of the tribes of Israel usually numbering ten. However Judah also included the tribes of Judah, Benjamin, Levi, Dan and Simeon. 1 Samuel 11:8; 2 Samuel 20:1; 1 Kings 12:16
Symbolism
When Ahijah took his garment and tore it into twelve pieces and gave ten of the pieced to Jeroboam it was to symbolise gesture that ten of the tribes were being handed over to Jeroboam's rule. 1 Kings 11:13, 31-32 Two tribes were technically left for David's line. But as has been mentioned there were more tribes left with Judah, indicating that the object lesson of Ahijah was only meant to be understood symbolically. It does not mean that Ahijah could not count, but simply wanted to make a symbolic point. Ten is the number of completeness compared to the single tribe of Judah which included the tribe of Benjamin in its singleness. Levi was never counted in the political classification of tribes and was included under Judah's roof. Simeon was geographically located so far south that it was unable to join Israel and be effectively ruled, so it joined Judah. Joshua 19:1-9
The Northern portion of Benjamin fell to Israel including the cities of Bethel, Jericho and Ramah. 1 Kings 12:29; 16:34 In order to balance things off a portion of the tribe of Dan went under Judah's rule. This territory included the cities of Ziklag, Zorea and Ajalon. 2 Chronicles 11:10; 28:18 In 957 B.C. the population of Israel is recorded at 3,500,000. 2 Chronicles 13:3 It was not a simple matter of ten tribes in Israel and two in Judah. It was actually more like nine tribes and these were not complete which belonged to Israel. Ahijah's object lesson was not to give the exact number of tribes but rather to show the general proportion of the division of the kingdom.
Religious Condition
The Kingdom of Israel (all twelve tribes) was divided into two kingdoms by God as a punishment for idolatry being introduced into David's household by Solomon's wives. In this way the entire nation was preserved from the influence of idolatry. Israel to the north continued in idolatry under the innovations introduced by Jeroboam I while Judah to the South was forbidden to stop the tribes from revolting from Israel.
With the formation of Northern kingdom under Jeroboam I there was a separation from the sacred place of worship in Jerusalem. To overcome this deficiency Jeroboam invented his own system of worship. He knew Israel was obligated to worship but sinned in the details in setting it up. He set the place of worship to be Dan and Bethel instead of Jerusalem. He drew the priest from the people instead of from the tribe of Levi. He changed the month that the feast of tabernacles was to be celebrated. He brought back the cow as the symbol of worship that was used by Aaron in the wilderness at Mt. Sinai. 1 Kings 12:28 The whole house of Israel was taken into exile by the Assyrians as a result of her never-ending Idolatry.
In the providence and purposes of God Judah was separated from Israel in order to preserve the integrity of the worship of Yahweh. 2 Chronicles 13:9-11 The majority of Judah's kings were godly while Israel did not have one king that was faithful to Jehovah.