War of Heaven

"Now war arose in Heaven, Michael and his angels fighting against the Dragon. And the Dragon and his Angels fought back, but he was defeated and there was no longer any place for them in Heaven. And the great Dragon was thrown down, that ancient serpent, who is called the Devil and Satan, the deceiver of the whole world – he was thrown down to the Earth, and his Angels were thrown down with him."

The War of Heaven is the conflict that rose between the Heavenly Loyalists and Lucifer's fanatical underlings during the creation of the worlds. The war saw only a single battle in Heaven, though Uriel remarks that it is still waged to this day, though throughout the cosmos, over the souls of Mortals.

Beginnings
"We were the first to be created! Why do the lowborns claim all the attention! Do you accept these lies, my brothers and sisters?! Do you accept the explanations of all these liars?! Of all the corruption?! Of this... False God?! -Lucifer, rallying his people to wage war on Heaven.

When Yahweh explained his plan of the creation of life to his Archangels, Lucifer was the only one to protest to it. He openly voiced that he should be the one to be the Messiah and lead God's children, but secretly, Lucifer despised the idea of having to bow to mankind, loathing his second-place in the eyes of God to a secondary children.

As time grew, as did Lucifer's impatience and pride. He overlooked the creation of the Earth, step-by-step, mineral-by-mineral, dro-before-drop. Becoming a master of the sciences and crafts God performed to create with, watched on with careful attention as the first Man was created, in his Father's image, just as he was. But Lucifer grew to understand a separate power from God's Sephiroth; the Qliphoth, which he dubbed capable of combating God's power and corrupting his supposedly "perfect" children.

When Leviathan was cast down to remain, shackled beneath the sea until the time of reckoning came, Lucifer secretly consoled the beast and nurtured its hatred of God and Man. He also began plotting alongside his allies, notably Beelzebub, Paimon, Azazel, Ashtaroth, Belphegor, and Asmodeus. With Amon, he managed to trick and force cooperation upon him. These Angels, as well as others who became increasingly loyal to Lucifer, were secretly experimented upon through Sin energy and the power of the Qliphoth.

Lucifer also experimented on himself, as well as introduced the power of Magic into the world, excusing that he thought it to be God's Will.