The Zhentarim, also known as the Black Network, is a group of ruthless mercenaries. Zhents, as they are known, will hire on to almost any job if the money is right, regardless of morality. Originally a secret society the Zhentarim grew bolder and bolder in the openness of their activities, especially in the area around their greatest stronghold Zhentil Keep.
That all came to an end in DR 1379: prophetically named the Year of the Lost Keep. Zhentil Keep and the Citadel of the Raven fell under the assault of the shadow magic wielding denizens of Anaroch known as the Shadovar. They devastated keep, city, and network with their fell magic in a single glorious conflagration. It is in that onslaught that Fzoul Chembryl, leader of the Black Network and the Church of Bane is believed to have perished.
Lord Kyoji’s Kolosari fought against the Shadovar when Zhentil Keep and The Citadel of the Raven were brought low. They also participated in the counter strike that briefly united the whole of the Moonsea under the Banner of the Coronal Protector of Myth Drannor Ilsevele Miritar. United they drove the Shadovar out their holdings in Zhentil Keep and the Citadel and back into the Anaroch Desert. A loose alliance remains between Shiminoseki and the elves to the south, but the other cites of The Moonsea area would just as soon forget they had any part in such an alliance.
The reign of the Black Network though wounded is far from ended. The wealth of the organization was spread far and wide through out the north of Faerûn and many other strongholds of the Zhentarim still exist through out the world.