Creation- the Realms were created. There was nothing, then there was something. Many of the powerful Archangels and Demon Princes(though they were still Angels then) were involved in this process, especially the elemental ones.
Eden- With the creation of humanity, there was a debate amongst the Angels as to whether humanity deserved the special place in the universe it was granted. God consented to an experiment, a test to show what humanity was like. Though one of the first test subjects opted out(Lilith), the experiment went forward. However, someone interfered in the guise of a serpent and the experiment ended without conclusion and with increased strife in Heaven.
The Rebellion- Shortly after Eden, things came to a head in Heaven. Lucifer, joined by a number of angels, entered into open Rebellion against God. They killed the Metatron and a number of other Angels, but ultimately, were cast out of Heaven, Michael personally throwing Lucifer out. The rebel Angels were trapped apart from the world.
The Reemergence of Demons- then, long after, the angels emerged, transformed from their imprisonment and rebellion into demons. The War began with this re-emergence as Demons sought to prove the point of their rebellion on Earth.
The Trial of Michael- In the wars against the Demons and on Earth, Michael fought fiercest of all, never retreating and being covered in honors. Dominic, worried Michael was usurping the worship owed to Heaven, accused Michael of Vainglory and he was tried before the Council of Seraphim. While he was found guilty, God intervened and pardoned him. Since then, Michael has not trusted Dominic.
The Rise of Christianity- During this period, the second Abrahamic religion was founded, greatly expanding the reach and goals of the Heavenly Host. Yves arranged for Gabriel to deliver the annunciation. Some Archangels took to Christianity quickly, others remained skeptical.
The Trial of Gabriel- After the rise of Islam, Dominic grew suspicious of Gabriel and suspected she had inserted her own opinions and perspectives into the Quran rather than the pure divine revelation. Gabriel was accused of Heresy and nearly tried before the Seraphim Council before Yves talked Dominic out of the full trial. In the aftermath, she abandoned her home in the heart of Heaven for a Volcano on the edge of the Marches.
The Purity Crusade- As Judaism flourished and Christianity and Islam began to spread across the world, Uriel, the Archangel of Purity and the leader of Heaven’s armies, set out on a crusade to purify the world of other gods and creatures. Their crusade eliminated many Pagan gods across the Corporeal and Ethereal Realms, the surviving ones made deals with Beleth, the Demon Princess of Nightmares, for protection and found refuge with Hell. Finally, Uriel was put on trial for this action but recalled to the Higher Heavens by God before its conclusion. They have not been seen since.
The Crusades- The Crusades brought about a time of crisis for Heaven and that crisis led to serious changes. The conflict between Christianity and Islam became a major source of tension between Archangels. After an incident, which rumors say involved Khalid and Laurence on opposite sides in a battle on the corporeal realm, that shook the heavens in level of disturbance, the heavenly hosts were recalled to the celestial realm and the Balance was instituted.
The Balance- Since the Crusades, miracles on the corporeal realm have grown quiet as the forces of Heaven and Hell have moved from open conflict to subtle maneuvering, limiting their involvement. New Archangels and Demon Princes have arisen to shepherd new human innovations and philosophies. Religion has taken many humanistic turns, guided primarily by mortals.