The roots of the Order lay in the Lore of the original Inhabitants of eastern Eriador, especially Rhudaur.After the Fall of Beleriand many refugees had returned to Eriador and made themselves rulers of related tribes.One of these Tribes was known as the Arvandor and ruled what was later known as the Trollshaws.
When the Númenóreans returned to Middle-Earth and the Elendili started to colonize Eriador they fought the Dark Cults that had evolved in Rhudaur at the time and subjugated the Arvandorian Tribesmen, but diverse superstitious traditions survived amongst the Eriadorians.
In the 13th century a man called Balsha the Prophet appeared in Eriador, preaching a new religion. He was quite sucessful in winning adherenty to his strange cults among the Men of Angmar and Rhudaur. After the Men of Eriador became more and more alienated with their Dúnedain Rulers, Angmar arose and claimed itself a free Kingdom. As Angmar had not been officially a part of one of the three Kingsdoms, its claim was widely accepted or at least tolerated by the three rivaling Kings of Arthedain, Cardolan and Rhudaur, everybody hoping to have Angmar as a possible supporter rather than a rebellious province drawing attention and military forces from more important areas.
Balsha´s teachings and the ancient traditions became the foundation of the Cult of the witch-priests of Angmar, who served a strange pantheon of Spirits.Their Head was a man called by the Name "the Ongûliun", a high-priest first serving as formal Ruler of Angmar. About the year TA 1300 the Ongûliun revealed the Witch-King as a prophecised King, who after ceremony, became the absolute Ruler of Angmar, with the Witch-priests as his Enforcers, Agents and ruling caste.
The Ongûliun was assisted by three to five high-priests, the Gûlmathaur, and three to six high-Generals or Murnairtur led by a chief-Murnairtur, every Murnairtur again was assisted by five Ashâkturi (Ang.: "Marshals") who each commanded two Burzâkturi (Ang.: "Lieutenants") everyone of whom commanded four Grîshakturi (Ang.: "Captains").
The Teachings of the Witch-Priests
The Key-figure of the Angmarean-Cults were the Teaching of Adanil, the "Friend of Men" or Arahoth (or Aradain), the "King of Men", a messianic figure. In the inner circles of the Cult this anticipated deity was also known as "The Lord of the Night", "The Lord of the Night and the Moon" or "The Lord of Night and Sorcery". He was also known as "The Lord of Death". The idenfification of the Edainil with the Necromancer of Dol Guldur was not openly revealed and only known to the highest circles of Angmar's clergy.
The War of the Ring
Some time before the War of the Ring Mordirith and Agandaur had come to Angmar via Gundabad and had brought a small group of Acolytes with them , starting to convert local Hillmen and Angmarrim.These Cultists of the Iron crown posed as pious monastics, tilling the fields and erecting new Shrines and small communities within the vales of Angmar trying to slowly built up a sizeable force behind the back of the Elves of Rivendell and the Rangers of the North.While not having a large Army behind them they still hoped to prepare a new rise of Angmar by uniting Hillmen, Orcs, Trolls,Angmarrim and Jörkyn under the Cult of the Iron Crown to gather an army that could cause the Elves and Dúnedain enough troubles to distract them from interfering with more important dangers in the south.