-Basic Timeline-



1010 BPA – The King of Soul Society orders a task force be formed for the protection of Soul Society and the elimination of the hollow threat.
1000 BPA – First Shinigami Academy founded by Cato Novius Longinus to train potential shinigami.
800 BPA – The initial seven squads have their Captain seats filled.
754 BPA – Captain Sextus of the 3rd Division discovers a breach in the Death Stone barrier that surrounds the Seireitei. Causes remain unknown.
750 BPA – More breaches are found along the Death Stone barrier and security is heightened in the Seireitei for the protection of the people within.
740 BPA – It becomes clear that there is a traitor among the Captains who has been leaking information to powerful hollows about where the wall is weakest. Suspicions are high but there is no conclusive evidence pointing to anyone.
739 BPA – First hollow sighting within the Seireitei, it was a Gillian and easily taken down but people are frightened.
720 BPA – Captain Arria of the 2nd Division heightens the number of guards around the walls and is praised over the next few years because of the decrease in wall breaches.
650 BPA – Captain Arria is found murdered in her office and her Vice-Captain is unable to assume her spot due to emotional trauma.
600 BPA – Hollow attacks on Earth are increasing but wall breaks are at a minimum. Because of the increasing number of injuries the 5th Division is split into the current 4th and 5th Division so that one could focus entirely on medical needs. All division numbers past 5 are pushed up one.
517 BPA – Captain Severtus of the 7th Division murders Captain Umistu of the 6th Division before feeing Soul Society. It become clear that he was the one responsible for Captain Arria’s death as well as the leaking of information.
490 BPA – Soul Society is attacked head on by a large force of hollows lead by two Vasto Lorde, an Arrancar and Captain Severtus. This is the start of the Great Hollow Wars.
475 BPA – Captain Cato clashes with the traitor Severtus just outside of Soul Society and kills him at the cost of receiving a mortal wound. His Vice-Captain Shigekuni Yamamoto takes his place and leads the attack.
400 BPA – A 9th Division is created this bunch were all strong fighters who all had a common goal of protecting the things they love. It would later become the 13th Division.
323 BPA – Captain Sextus kills one of the Vasto Lorde leaders in combat, he is barely saved from dying by the Vice-Captain of the 4th Division Retsu Unohana.
307 BPA – The Captain of the 5th Division Sōsuke Aizen, kills the Arrancar Fang Irontail, so only one the Vasto Lorde Diamonddrill Jaberhawk remains.
250 BPA – The forces of hollows start to swell. It seems as though they are better controlled under one leader than four. Soul Society calls on the Quincy to help them repel the attacks.
239 BPA – The Quincy finally answer the call and send some of their best warriors to help in fighting off the hollow menace.
110 BPA – The Great Hollow wars end when Captain Yamamoto kills the final Vasto Lorde leader with the help of the Quincy Lord Eiji.
1 AA – The rebuilding is finally completed with the establishment of a larger Shinigami Academy as well as the Gotei 14. Many of the old Captains retire and their places are filled by newer members. Ikkimaru Shurajou was immediately chosen for the seat as Captain in the 14th squad for his prowess in the Great Hollow Wars.
25 AA – Two of the first seats filled are students of Captain Yamamoto, Ukitake and Kyōraku are made Captain of the 13th and 8th Divisions respectively.
542 AA – The Shinigami and the Quincy have a falling out and communication between the two people ceases almost completely. Ikkimaru tries to keep ties with them.
620 AA – Captain Kisuke Urahara begins research on devices called Gigai that would allow Shinigami to blend into society on Earth more easily, and effectively help to better protect it.
660 AA – The first Gigai are put into use and Captain Urahara begins research on yet another invention right away. Something he calls the Mod-Soul.
812 AA - The first working Mod-Soul is put into use, it revolutionizes the system of using Gigai on Earth.
1398 AA - Ikkimaru loses his patience with the Central 46, Commander-General Yamamoto, and the King of Soul Society. He lobbies for changes in Soul Society but he and his squad are seen as a threat to the peace and way of life, thus are officially disbanded.
1401 AA - After two and a half years of negotiations that lead to random skirmishes between the 14th Squad and the other 13 squads a final battle is held and over half of the 14th squad is killed, however 68 seated members of the 13 squads, and two lieutennants were killed. The Captain of the 6th squad fell to Ikkimaru's Bankai in the end. The remaining members were so worn out from battle that they were all captured. Ikkimaru struggled to the very end claiming that this was "unjust." They had mercy on him and the six other remaining members of the squad and instead of killing them they were bannished to Hueco Mundo, thought never able to return.
1402 AA - An order is passed that no shinigami is to mention the 14th squad's existence. To even allude to it was a crime.


[Notes: BPA – Before Present Academy and AA – After Academy. We can assume that the Academy was started at the start of what we refer to as AD]


Note: Quoted from Lord 0thello, edited by shidobu cloud