Disclaimer: I do not own Harry Potter brand. Otherwise I wouldn't bother to write fanfics.
Dumbledore turned and walked back down the street. On the corner he stopped and took out the silver Put-Outer. He clicked it once, and twelve balls of light sped back to their street lamps so that Privet
Drive glowed suddenly orange and he could make out a tabby cat slinking around the corner at the other end of the street. He could just see the bundle of blankets on the step of number four.
"Good luck, Harry," he murmured. He turned on his heel and with a swish of his cloak, he was gone.
A breeze ruffled the neat hedges of Privet Drive, which lay silent and tidy under the inky sky, the very last place you would expect astonishing things to happen. Harry Potter rolled over inside his blankets without waking up. One small hand closed on the letter beside him and he slept on, not knowing he was special, not knowing he was famous …"
"Harry Potter and the Sorcerer's Stone, chapter 1."
Not knowing that people all over Great Britain were celebrating end of the war, while Leader of the Light left 1 year old orphan at door steps in the cold November night.
Next few days, wizarding society of Great Britain went into full recovery and trial mode. All suspected Death Eaters were questioned, some bribed their way out, some didn't. With Dumbledore's forgiveness and second chance policy it was more the former that the later. Only the most heinous criminals were thrown in prison. That of course were crimes against purebloods like Longbottoms and Bones, after all who cares about how many muggles died during the time of Voldemort terror? Killing and torturing old families however were not that easy to forgive. Of course common folks didn't know any of this or if knew they just kept their heads low, being the sheeps they were. Business start working again, and all…
All the while little Harry spent in Accident and Emergency Department of Little Whinning local hospital after catching pneumonia during his night stay at doorsteps. Naturally Petunia and Vernon didn't pay any attention to the freak at the first day, except for screaming and trying to decide how they can get rid of him. As they discovered on the second day that Harry was literally burning from high temperature they panicked and immediately dropped him at ambulance, explaining how this child occurred at their footsteps, and taking their precious Dudley to full medical check. Dudley was fine, Harry was not. Catching pneumonia at such young age, together with severe magical exhaustion from earlier encounter with Killing Curse and having his living and magical energies draining by Voldemort horcrux in his scar meant that poor child wasn't even able to recover from earlier trials, far less fight disease. Being an infant meant doctors were limited at what they could do to help with medicines and procedures. As it is, little Harry Potter died at resuscitation department of the local hospital 4th of November 1981. It was a wonder he survived that long, but in the end, disease, exhaustion and drainage killed child before he saw his second winter. Ancient house of Potter became extinct. Heritage of old family and brilliant brains of Lily Evans didn't protect child from bigoted and egoistical society of followers, nor from great Albus Dumbledore who always knew better than others.
Child's death is a tragedy on itself. However, little Harry's death was only the beginning of tidal wave that buried whole world. Energy of his death and any magical essence that were left in his body fed parasite-horcrux , combined with it's own magic accidental horcrux disengaged from its dead host and merged with Voldemort's main soul. Distance between them were irrelevant, as they were still parts of the same soul. Receiving massive energy burst from child's death together with knowledge of what happened, Tom Riddle was able to conjure himself a new body. After which the flame of war burst even stronger. Death Eaters inspired by their master immortality and magical power became even more ruthless, with Dementors sided with Voldemort most faithful and dangerous servants were free in no time. Ministry held for two weeks, but fell as werewolves and vampires joined Voldemort. A new Dark Era began…
However, magicals forgot the time they were living in. Muggle no longer were using swords and bows. Modern weaponry became more powerful and dangerous for everyone. As Death Eaters and dark creatures got free reign at the streets, it took 3 days for muggles to discover magical world and creatures and terror they were inflicting. Within hours governments all over the world were notified and muggle army started to fight back. Magical received severe losses because of their arrogance and little to no knowledge about muggles. However muggle were defenseless against mind controlling spells, ability to travel at will at any location and huge arsenal strong magical fighter possessed, making him extremely dangerous in his versatility. Trained mage was small army by himself, able to do huge variety of operation alone from sneaking into bunker and assassinating leaders to destroying targeted areas.
Muggle's had numbers, technology and science. Magicals had their abilities. The war started in British Islands spread around the world in less than a week. Weakest and stupidest magicals and muggle commoners died first. After that every country were fighting on their own territory, first by curfew and patrols, using any technological identification and surveillance possible, killing those who didn't pass. Fireweapons, bombs for known magical locations, acids, gas, laser weapons… everything was used mercilessly slaughtering anything magical.
Assassinations, destruction of refugee camps and military bases, ammunition storages, impersonation and mind controlling. No muggle was able to look at another without caution. Wives killed husbands, soldiers returned from patrol to slaughter families and higher officers. No psychological test or inspection worked. No one was protected. As the conflicted escalated, the heavier and more destructive and dangerous weapon were used. Bio and nuclear weapon, dark magical curses and rituals, demon summons and necromancy. In the end there was nothing left. What once was a blue-green planet full of life turned into black desert with no life. Ash and smoke filled the air from land to troposphere. Hydrosphere turned into radioactive acid. Once proudly rising to the sky buildings turned into sand, vegetation burned with its roots kilometres deep into the soil. Any life form died from bombing, diseases, dark magic. Demons and dead now ruled the Earth with its very living energy turned into demonic and necro energy.
The End.