Hell was complicated. Being entirely underground meant that there was a finite amount of space. As more and more people went to Hell, overcrowding was inevitable. The Devil's solution was straightforward: every time a new person went to Hell, it expanded. It's elegant and humans balk at the concept (always a nice bonus). Sometimes, a bored demon would torture a physicist by showing them how Hell expansion works and not allowing them to tell anyone.
Angels and mortals won't tell you this, but demons like rewarding good behavior. Torturing your fellow hellmates is fair game, but demons will find ways to make your torture crueller if you waste their eternal time. The Fallen Angel himself built a handful of infinitely-stocked cigar lounges for when the humans got breaks (breaks help prevent them from becoming numb to the torture). Smoke any of the cigars and you'll have maggot eggs lining your mouth and throat. It's pretty basic, but the real kicker came when he told the humans that he made a dozen cigars that can bring people back to life. Angels can't lie. A few hours later, some woman from Heresy was floating up all the circles on a beam of light. To this day, you can't go half an hour without seeing people hacking up maggots.
The other 11 cigars are in the Devil's desk drawer.
Torture devices like that are excellent, but developing personalized torture devices for an ever-increasing number of people is a bit of a logistical problem. For a long time, demons would just dip people into the Pit of Eternal Fire, but that meant that they pretty much had to ignore small infractions (which are their favorite to punish) and don't have any way of rewarding good behavior.
While the Devil's cigar trick was clever, his real stroke of genius was the Dynamic Evil Valuation In Length (DEVIL) system, which took human behavior and translated it into a length. That length was added or subtracted from that person's Hell expansion radius. Good behavior made your corner of Hell roomier, while bad behavior would have you screaming into your hellmate's mouth. And it was collective. Regardless of how much space they had, the humans spent their eternity wondering if they were getting screwed over by some crappy person they'd never met. Needless to say, the Greed and Wrath people hated it. Before the DEVIL system, all the demons had left the nationalism branch of Wrath to let the humans torture each other forever. The demons came back for a little bit, but only to watch what would happen as their little thunderdome started to shrink. It was bad (by which I mean good (by which I mean highly entertaining)).
That was the first sign of the problem.
Hell was getting smaller. Way smaller. No one noticed at first. Then, it seemed like a fluke — or maybe an error with either the Hell expansion or DEVIL system. Things got checked and double-checked and everything was in order. The problem was the humans.
They were up to something.
Remember how bad behavior could shrink your expansion radius? Apparently they'd coordinated to all get their radii as low as possible. They'd agreed to be bad. The Devil didn't understand why they would want to do that, but he knew one thing for certain: whenever humans got together like this, someone ended up in a lot of trouble. Maybe it would be him, maybe it would be them, maybe it would be the folks in Heaven. The Devil's weapon is temptation, and even he couldn't resist letting this play out just to see who would take the fall.
Soon enough, none of the demons had to work anymore. Not like there was anything they could do within the compressed throngs of people. Pushing and kicking and gasping sweaty air, the crowds were squeezed tighter. Words were lost amongst the noise. The air between bodies disappeared. The edges of people pressed against one another, becoming wrinkles in a single, screaming disc. People cannot die again in Hell. Instead they compress beyond mortal limits, bodies stretching vertically, blood swelling into any limbs lifted above the sinful masses.
And then
THWUP
Like a great cavernous cannon, the only part of Hell left was a shrinking tunnel pointed straight towards the entrance. The humans, the demons, the cigar lounges, everything jettisoned out into the mortal world and scattered across the lands. By the time the Devil had dusted himself off, the High Seraph was already waiting, shading itself with its six feathered wings.
"What the Heaven is this?" the angel asked.
"I... um... uh... Hell peace?"
"Hell peace?"
"Hell peace. It's like world peace, but... in Hell."
The High Seraph glanced around. "Doesn't look very 'in Hell' to me."
"Well, it was in Hell. Initially. My point is they all put aside their differences. They worked together! No one on Earth can do that!"
"That's great, and I'll appreciate that later. Right now, I have to kill all these people again and you have to make sure that they can't get out of Hell again."
The Devil stopped to do some mental math. "I like the idea, but I think most of the people aren't going back to Hell."
The High Seraph narrowed its eyes.
"I mean, think about it: everyone's back to life, so they get a second chance at judgment. And Hell peace. Hell. Peace. Most sins are small potatoes compared to that. Plus, you can fight with your spouse every day and still get purgatory. I'd be surprised if a lot of people did go back."
They both said nothing for quite a while. The High Seraph's wings twitched.
The Devil traced a glowing red circle with his heel. "So... I think I'm going to head out. I've got a lot of cleaning up to do. Back home, I mean. I'll be sure to take the demons with me. And the cigar lounges. But, um... good luck with everything! It was nice seeing you again. It's certainly... been a while."
The High Seraph said nothing.
It was a good day to be the Devil.