Soul War

The Soul War (魂の戦争, Tamashī no Sensō) is an ongoing conflict between the Kyuushoku and those involved in the Tetra Alliance. Having started in 2043, it has spanned over the course of eight years, and there is little to indicate that it will end soon.

Prelude
The Kyuushoku, who have been preparing for an attack since the late Iron Age, begin to send small teams of Kaisou into Japan. Their primary task is to gather intelligence on the Shinigami stationed around the country; their secondary task is to kill any Shinigami on-sight after recording the required data. These deaths draw the Gotei 13 's attention and an investigation is launched. They catch and detain three of the Kyuushoku's soldiers, and the organization's existence is revealed. The Gotei immediately declares war on the Kyuushoku.

Early Stages
The Kyuushoku continues to send small teams of soldiers into the World of the Living to fight the Shinigami and cause chaos in the humans' cities. The Gotei also deploys teams of soldiers to deal with this new threat. The fights are small and the casualties are miniscule; neither side is fighting at full force.

The Battle of Karakura
On September 6, 2043, Clans Lila and Baltas attacked Karakura Town. They catch the Gotei off-guard, and decimated over half of the city before Shinigami reinforcements from Divisions 6, 13, and 10 arrive. Just hours into the battle, it is deemed a lost cause. The surviving citizens in Karakura are rescued by members of the Sixth Division and escorted to Soul Society while the remaining Shinigami hold the enemy at bay. The fight lasted for a total of eighteen hours, but almost all the humans in Karakura were killed alongside several hundred Shinigami. Both Ichigo Kurosaki and his father Isshin died while escorting humans to the Seireitei.

The Battle of Zaraki
Due to the previous battle, the Kyuushoku is now able to pinpoint the area of the Dangai that the Shinigami use to cross between the World of the Living and the Soul Society. Clans Lila and Baltas launch their second attack on October 1, 2043. This time, however, they invade the Rukongai. Divisions 9, 10, 11, and 13 are deployed, but the extra numbers do not help. They are practically slaughtered, and backup from the 2nd and 3rd Divisions is sent out to help in the fight. Unfortunately, the Gotei cannot keep their ground, and Rukon Districts 80 through 65 are destroyed. Kenpachi Zaraki, Captain of the 11th Division, is killed in this battle. The fighting ends in a week.

The Battle of the White Desert
During the Battle of Zaraki, Clans Akai and Grey are sent to attack Hueco Mundo. However, the Hollow are better prepared; within a day, the Kyuushoku Clans are forced to retreat lest they be wiped out. It is after this battle that Tier Hallibel and Coyote Starrk attempt and fail to form an alliance with the Gotei.

The Battle of Sabitsura
The Battle of Sabitsura began on November 17, 2043. Clans Lila, Baltas, Grey, Akai, and Azul launched a full-scale attack on what remained of the Rukongai. Almost every Shinigami was deployed into the field, and less than half returned alive. To this day, there has been no battle as destructive and bloody as this one was. Head Captain Yamamoto, Lieutenant Sasakibe, and Lieutenant Ohmaeda were all killed, alongside Hachigen Ushoda and Love Aikawa. Captain Hitsugaya was severely wounded and forced to retire from his position due to the injuries he sustained.

After the battle, the Gotei contacted the Arrancar and agreed to form an alliance. The humans and Vizard also signed the treaty, and thus the Tetra Alliance was created.