http://revach.net/article.php?id=3498

Section: Tanach   Category: Yirmiyahu
Yirmiyahu Part 2: A Competition Of Wickedness, Yisroel And Yehuda
At this point in history, the ten shevatim of Yisrael had already been sent into galus. The ten shevatim, who had lived in the north of Eretz Yisrael had seceded from the south, and had been ruled by a succession of evil kings, who encouraged them to serve avodah zara.  Hashem sent neviim to warn them, time after time, to improve their way, but to no avail.  Ultimately, Hashem sent Ashur (Assyria) to punish them, and the ten shevatim were sent into galus and lost until the end of days.

Unfortunately, the remaining shevatim were now following in the ways of the ten shevatim, and even exceeding their wickedness.  Hashem told Yirmiyahu, “Yisrael had committed adultery.  I sent her away and I gave her a bill of divorce, but treacherous Yehudah, her sister, did not fear, and she too went and played the harlot.”

The “divorce” of Hashem from the ten shevatim is referring to the fact that there will never again be a king from the ten shevatim.  During the times of Moshiach, the kings will all stem from Beis Dovid.  Therefore Hashem did not “divorce” Yehudah, but merely sent her away and will eventually “take her back” – when their kings rule over Yisrael once again during the time of Moshiach.

“Yisrael has proven herself more righteous than treacherous Yehudah.”  The Radak tells us that Yehudah engaged in so many sins that her sister Yisrael now appeared righteous in comparison.  Yehudah stooped to actually bringing their idols into the Beis Hamikdash and nullifying the avodas hamikdash.  King Achaz commissioned the construction of an altar, modeled on the altar in Damascus.  Under his rule, the lighting of the menorah and the burning of the ketores were halted, and Achaz himself passed his children through fire in his service of avodah zara.  King Menashe, who was even more wicked than the Amori, also passed his children through fire, and practiced all types of sorcery and other forbidden practices. His service of avodah zara caused Bnei Yisrael to sin as well. In addition, he murdered so many innocent people that he filled Yerushalayim from one end to another with their blood.

With kings so evil, it is not hard to understand why Yirmiyahu’s rebukes went unheeded.  These evil kings caused widespread sin and worship of avodah zara, which became firmly entrenched among Klal Yisrael, and made it very difficult them for to do complete teshuvah.