Note: The memories of Johnny Silverhand relived in the events of Cyberpunk 2077 are not accurate to what really happened in 2023 as per the lore. See Flashbacks for more information.
On August 20, 2023, an incursion team led by Solo Morgan Blackhand and Rockerboy Johnny Silverhand attempted an infiltration mission to steal/destroy the Arasaka Secure Reliquary Database inside Arasaka Tower in Night City. During the assault, an area denial nuclear device, or "pocket nuke" was planned to be detonated in the building, with the planned area to absorb the impact of the blast and prevent massive destruction. However, due to interference by Arasaka and Adam Smasher, the nuclear device prematurely detonated on the 120th floor, 366 meters above the ground, obliterating Corpo Plaza and a large portion of City Center, and scattering radioactive fallout across the rest of Night City. The blast instantly incinerated over 12,000 people in the vicinity of Arasaka Tower and fatally injured upwards of half a million more. Another quarter million died in the resulting aftermath over weeks and months.
In the public's eyes, the reasoning for the nuclear detonation is never uncovered. Some believe it was Militech's overzealous desire to crush Arasaka, while others believe it was an area denial weapon meant to protect the Arasaka Towers.
Within hours, then–US President Elizabeth Kress nationalized Militech through the expedience of their CEO, General Donald Lundee, and his reserve commission. Militech is placed thoroughly under the control of the still sizable United States military, and banished all Arasaka forces from the continental US under the threat of a retaliatory strike on Arasaka's Tokyo headquarters. Other nations swiftly followed the US's lead, nationalizing and/or interdicting assets of both participants of the War.
Database Entry (2077)
The only undisputable fact in this story is the date, 20th August, 2023 - the day a nuclear explosion obliterated Corpo Plaza and a large chunk of City Center. The rest is pure speculation, gossip, lies and conspiracy theories, all the way from number of causalities to those responsible for the attack. The most famous version - widely disseminated by corporate PR machines and tickled down through the media - tells of an unidentified terrorist group that was responsible for an armed assault on Arasaka Tower followed by the explosion. But does anyone really take corporate press releases seriously anymore? Take some of the more intriguing theories circulating on the streets today - that it was an inside job in an attempt to escalate the conflict between Arasaka and Militech followed by an elaborately orchestrated cover-up, or the results of a failed experiment that spiraled out of control in a secret lab somewhere under Arasaka Tower. How much of it is true? Most likely we'll never find out, and even if we did, it wouldn't bring back the victims of the tragedy.