All the promises of scripture were made to the descendents of a man named Israel (originally named Jacob) who had 12 sons. Two of Israel's grandsons were included in the promise as well. One of Israel's sons, his fourth, was named Judah.
Originally Simeon was pre-eminent because he was the first-born. However his mantle soon fell to Joseph and was passed on to one of Joseph's sons (Ephraim), a grandson of Israel, because Joseph rescued his brothers in a time of severe famine.
After the tribes of Israel escaped Egyptian captivity and arrived in the land promised to them by God, the religious capitol of the nation was moved out of Ephraim (Bethel) and taken to Judah (Jerualem). This happened when God chose David to be king of the tribes, because the priests of Bethel were misusing their authority.
After the death of Solomon, a serious contention for leadership over the 12 tribes arose and a gigantic schism broke the unity of the nation into two parts. Ten tribes splintered off to rule the northern provinces and set up a temples at Bethel and Dan, while the tribes of Judah and Benjamine remained loyal to Solomon's son (the royal line of David) and continued temple worship in Jerusalem at the Temple of Solomon.
The ten tribes, weakened by the disunity, were no match for their foes. Foreign invaders came in and decimated the countryside. Defeated by the Assyrians, the Israelites of the ten tribes were marched off into captivity to the lands of the north. In their place, the Assyrians repopulated their land with foreign immigrants. The tribes of the north were never seen again. They simply vanished into the genetic framework of mankind.
The Jews felt that this disappearance was a sign from God that they, alone, were the favored of God. When Ezra defined the new Jewish religion, this idea of preeminence was one of the three major tenants of his Jewish theology. According to this doctrine, the promise of Abraham belonged only to the Jews which was alone considered the 'chosen race' of God.
The prophets, however, rejected this new and arrogant Jewish doctrine. God was a God of all mankind. The lost tribes would be found, the prophets said, and they would be called back by God to Jerusalem where they would return in great triumph. Not only would they return, but they would be given by God, the mantle of leadership over all the twelve tribes:
"Son of man, the citizens of Jerusalem (the Jews) are telling the rest of the House of Israel, that since the tribes of the north were sent away from God, that it is to the Jews that the land has been given as their domain. Say therefore, The Lord says this: 'Yes, I have sent them far away among the nations, and I have dispersed them to foreign countries...but I will gather them together from among the peoples, I will bring them all back from the countries where they have been scattered and I will give them the land of Israel." (Ez.11:14-21)
"The word of God told Jeremiah to go and shout these words towards the North: "Come back, disloyal Israel - it is God who speaks - I shall frown on you no more, since I am merciful. I shall not keep my resentment forever. Only acknowledge your guilt..." (Jer.3:12).
"See, the days are coming when I will raise a virtuous branch for David, who will reign as true king and be wise...so, then, the days are coming when people will no longer say, 'Praise Passover!', but 'Praise the Lord who led back and brought home the descendants of the House of Israel out of the land of the North and from all the countries to which he had dispersed them, to live on their own soil'. (Jer.23:5-8)
The Jews scoffed at these predictions despite the fact that they resided in their own scriptures. How, they argued, could a lost people ever be recovered? It seemed to them a ludicrous prophecy. Moreover, they had a vested interest in rejecting these passages of scripture because the Jews had no intention of sharing the mantle of leadership with another people.
The shepherds are the ones who have been stupid:
they have not searched for the Lord
This is why their whole flock has been dispersed.
News! News has come!
A mighty uproar from the land of the North
to reduce the towns of Judah to a desert... -Jer.10:21-22
This great ingathering from the north is the era of Christianity.
It features one House of Israel following Jesus, who is the David of scripture chosen by God; and a second House of Israel rejecting that leader and setting up alternative sites of worship in the Bethel's and Dan's of the world. This rejection was ordained by scripture because it creates a contrast that makes Jesus visible to the pagans. It guarantees that 2 "Houses" of Israel will continue virtually to the Last day.
"One section of Israel has become blind, but this will last only until the whole pagan world has entered, and then after this the rest of Israel will be saved as well." (Rom.11:25.)
Scripture promises that when the pagan reconcilation with God has been completed, the Jews will regain their sight and the two Houses of Israel will unite into a single people under Christ.
"In those days the House of Judah will unite with the House of Israel; together they will come from the land of the North to the land I gave your ancestors as a heritage." (Jer.3:18). The reference is to the Diaspora both will be called out of Babylon, the "Ten Lost Tribes" and the Jews as well.