The River Of Gozan
Gozan, derived from a root Hebrew word meaning to be cut off from the stone (ironically, as in a rock quarry, see also Rock Of Ages), was the name given to a region of Mesopotamia (today, Iraq) where the religiously-corrupt people of the northern Israelite tribes, the Kingdom of Israel (which, after the division of the twelve-tribes Kingdom of Israel in the time of Rehoboam, was not the Kingdom of Judah - see Jews At War With Israel and Where Is "Israel" Today?) were taken into exile by the Assyrians. The Habor River (2 Kings 17:6), a tributary of the Euphrates River, flowed though Gozan and was sometimes referred to as "the river of Gozan" (e.g. 1 Chronicles 5:26).
They "played the harlot after the gods of the peoples of the land"
The unfaithful Israelite tribes east of The Jordan River were the first to go, as a simple matter of geography, since they were already closer to Assyria:
"But they transgressed against the God of their fathers, and played the harlot after the gods of the peoples of the land, whom God had destroyed before them. So the God of Israel stirred up the spirit of Pul king of Assyria, the spirit of Tilgath-pilneser king of Assyria [see Ancient Empires - Assyria], and he carried them away, namely, the Reubenites, the Gadites, and the half-tribe of Manasseh [see Eastern Tribal Lands], and brought them to Halah, Habor, Hara, and the river Gozan, to this day." (1 Chronicles 5:25-26 RSV)
The people of the Kingdom of Israel west of the Jordan River were next to be conquered by the Assyrians, keeping in mind that the Assyrians never conquered the Kingdom of Judah (although they tried, see The Day Sennacherib Challenged God), whose territory was in the southern section of the Promised Land; that came over a century later, and was done by the Babylonians (see the Fact Finder question below):
"Then the king of Assyria invaded all the land and came to Samaria, and for three years he besieged it. In the ninth year of Hoshea the king of Assyria captured Samaria, and he carried the Israelites away to Assyria, and placed them in Halah, and on the Habor, the river of Gozan, and in the cities of the Medes."
"And this was so, because the people of Israel had sinned against The Lord their God, who had brought them up out of the land of Egypt from under the hand of Pharaoh king of Egypt, and had feared other gods and walked in the customs of the nations whom The Lord drove out before the people of Israel, and in the customs which the kings of Israel had introduced."
"And the people of Israel did secretly against The Lord their God things that were not right. They built for themselves high places at all their towns, from watchtower to fortified city; they set up for themselves pillars and Asherim on every high hill and under every green tree; and there they burned incense on all the high places, as the nations did whom The Lord carried away before them. And they did wicked things, provoking The Lord to anger, and they served idols, of which The Lord had said to them, "You shall not do this." Yet The Lord warned Israel and Judah by every prophet and every seer, saying, "Turn from your evil ways and keep my Commandments and my statutes, in accordance with all the law which I commanded your fathers, and which I sent to you by my servants the Prophets."
"But they would not listen, but were stubborn, as their fathers had been, who did not believe in The Lord their God. They despised his statutes, and his covenant that he made with their fathers, and the warnings which he gave them. They went after false idols, and became false, and they followed the nations that were round about them, concerning whom The Lord had commanded them that they should not do like them."
"And they forsook all the Commandments of The Lord their God, and made for themselves molten images of two calves; and they made an Asherah, and worshiped all the host of heaven, and served Baal. And they burned their sons and their daughters as offerings, and used divination and sorcery, and sold themselves to do evil in the sight of The Lord, provoking Him to anger."
"Therefore The Lord was very angry with Israel, and removed them out of His sight; none was left but the tribe of Judah only." (2 Kings 17:5-18 RSV)
Fact Finder: Did the Kingdom of Judah also fall because of their unfaithfulness to The Lord?
See Why Babylon?