In IY 1121 the fledgling Church of Mithras called a great council, the Council of Pader, in order to bring some standardization to it's beliefs and holy texts. The Council was attended by bishops of all the major churches across the The Thousand Isles and even representatives from as far away as Bawaaba and Valoria.
The council made many important decisions, that resulted in a far more homogeneous set of beliefs and a unified holy book. However several churches, most notably the ones from the Northern Reach and Valoria took exception to a number of these decisions and refused to sanction the outcome of the council.
As a result, the religion splintered, the majority of bishops forming the Orthodox Church of Mithras and a smaller set (mostly from the The Northern Reach) forming the Northern Church of Mithras, a division that exits until this day. The two relations between the two churches is cordial but strained.