The first salvo in the war, although only recognisable as such with hindsight, was the phenomenon nicknamed 'Block Mania' in the year 2103 AD (progs 236 to 244). A wave of internecine fighting surged through the streets, pitting city block against city block and even sucking Judges into the swirling maelstrom of violence. For no discernible reason the citizens were up in arms, and heavy artillery intended for repelling external foes was instead deployed against former neighbours. Anyone from a different block was fair game.
It was eventually discovered that the cause of the civil strife was a psychotropic agent in the city's water supply which increased people's aggression and tribal instincts simultaneously. The dissipated old roué Max Normal, who only drank shampagne and therefore remained completely aggression-free, was a vital part of this discovery. The water had been contaminated by Orlok, a spy from the Sov city of East-Meg One. Orlok compounded his offence by killing Judge Giant, Snr., a popular character whom many readers felt deserved a better death.
By the time the Judges had realised what had happened and developed an antidote to 'Block Mania' from Orlok's blood, it was too late. With Mega-City One drastically weakened by internal conflict, East-Meg One were able to launch a rain of missiles that destroyed almost half the city. When Mega-City One tried to fight back they discovered that the Sovs' city was protected by a force field made from a dimension warp: any weapons that hit it were sent to another dimension, where they annihilated a parallel Earth and its peaceful inhabitants. Mega-City Two and Texas City (the other North American super-conurbations) sat on their hands, afraid of Sov retaliation, and East-Meg One had boots on the ground in Mega-City One before you could say "synthi-cheese." Citizens and Judges alike were slaughtered by Strato-Vs (aerial units), sentenoids (martial robots) and rad-sweepers (huge tanks). The Big Meg's de facto leader, Chief Judge Griffin, was brainwashed by Sov scientists and went on television praising the Sov régime and urging the surviving citizens to submit to life under the East-Meg jackboot. It was Mega-City One's darkest hour.
However, all was not lost. Judge Dredd, one of an intrepid band of stalwarts fighting a guerrilla war against the Sov invaders, made Judge Griffin admit his lies before executing him while the television cameras were still rolling. He then escaped the city with a group of hand-picked assistants, including Judge Anderson, to take the fight to the Sovs. Through a combination of cunning and bravery the team managed to infiltrate a Sov missile silo, and Dredd pressed the button that launched a retaliatory nuclear strike on East-Meg One. Because the silo was so close to the city it was unable to raise its force field in time and 500 million citizens died, forcing the Sovs to surrender and withdraw from Mega-City One.
In many ways, what Dredd achieved was a Pyrrhic victory. The city has never recovered the size or the population it boasted before the events of 2103 AD, and thirty years later an East-Meg revenge attack led to the events of 'Chaos Day', in which a further 350 million citizens died. Some Judges blame Dredd's nuking of East-Meg One for provoking this retaliation.
Judge McGruder, who had fought valiantly against the occupying forces despite being injured, became Chief Judge after the Apocalypse War and compelled the survivors to join work gangs to rebuild at least some of the city. One of the things they erected was a memorial to the victims in the shape of a mushroom cloud, proving that, at least, the city's characteristic tastelessness was alive and kicking.
The Apocalypse War was written by John Wagner and Alan Grant, who felt that Mega-City One had grown far too big and therefore embarked upon the most drastic method of urban planning the world has ever seen, and drawn by Carlos Ezquerra. 'Block Mania' was drawn by Mike McMahon, Ron Smith, Brian Bolland and Steve Dillon. The saga was lettered by Tom Frame and Steve Potter, and it was later published by Hachette Partworks Ltd. as volume 36 of Judge Dredd: The Mega Collection.