The Deepground War is a military conflict in Dirge of Cerberus -Final Fantasy VII- in εγλ 0011, in which the Deepground emerged from the ruins of Midgar and wreaked havoc upon the world. The World Regenesis Organization (WRO) eventually pushed them back, but not in time to stop Deepground warriors from summoning the Omega Weapon that nearly destroyed the world. Vincent Valentine narrowly defeated Omega using the power of Chaos, and the war came to an end.
Shinra Electric Power Company established Deepground in Sector 0 as an experiment to improve the SOLDIER program. Initially a medical lab, it became a prison in which soldiers were subjected to a brutal training program. Children were born in Deepground and kept there, and ordinary conscripts were sent their against their will for testing. Deepground itself was divided into four sectors, all of which were ruled by the so-called Restrictors. The Deepground SOLDIERs received ranks according to their abilities, with Tsviet being the highest.
During Meteorfall, the Deepground became trapped inside Sector 0 as the surrounding walls collapsed around them. They would remain trapped for three years. During this time, Tsviets Rosso the Crimson and Azul the Cerulean rose up against the Restrictors. With the aid of Weiss, they seized control of Deepground.
Under the postmortem influence of Professor Hojo's mind through the Worldwide Network, the Tsviets sought to awaken Omega, triggering the birth of Chaos, which would send all life to the lifestream. Omega would absorb the lifestream and fly into space on a search for a new planet.
To achieve this, they would have to kill a large number of people with lifestream untainted by Jenova. This would trick the planet into thinking that it was in danger and summon Omega. With this plan, the Deepground started to dig their way out of their containment.
World Regenesis Organization
Following Meteorfall and the fall of Shinra, the World Regenesis Organization was created by former Shinra employee Reeve Tuesti. The purpose of the WRO was to serve as a transitional government while the world recovered from its recent ordeals. To protect the people, an all-volunteer military wing was established. The WRO was financed by an anonymous benefactor who is heavily implied to be former Shinra President Rufus Shinra.
Course of the war
The world got its first hint of the incoming menace when a television crew and an investigation team went missing while on an expedition to Sector 0. They became the first casualties of the Deepground War.
The Deepground initiated the war with a massive airborne assault on Kalm. The WRO was caught off-guard and although it eventually repelled the Deepground from Kalm, they failed to prevent a large number of civilians from being taken prisoner.
To the WRO, the victory was a minor one. Moving quickly, Deepground stroke Edge and Junon and again abducted a large number of civilians; in Junon alone, as many as 1,200 people vanished without a trace. This marked the beginning of a series of Deepground attacks all around the world. At some point, Deepground attacked Wutai, but the invasion was repelled by Godo Kisaragi and the Wusheng.
After learning of the Deepground's plan to summon Omega, the WRO mounted a large-scale offensive against their base in Midgar. While the WRO and veterans from Avalanche battled the Deepground on land and in the air, Vincent Valentine served as a one-man vanguard and advanced towards Sector 0 on his own to stop the summoning. He learned that Hojo was the secret mastermind behind the Deepground, but he failed to prevent the summoning. The WRO destroyed Midgar's eight mako reactors to prevent Omega from taking the lifestream. Vincent entered his Chaos form, took on Omega and prevailed. Chaos and Omega returned to the planet, and the remainder of Deepground was wiped out.