Magic King of Great Britain
Magical Dominance
1975
Growing weary of the prolonged conflict against the Ministry of Magic, Voldemort decides to change tactics. He takes his most skilled and powerful Death Eaters and ambushes Dumbledore. After a long battle, the Dark Lord finally strikes down Dumbledore and takes his wand as a trophy. Then he marches on the Ministry, using a large army of Dark Creatures (mostly giants, vampires, Inferi, and trolls) to overwhelm the Aurors and other Ministry officials. After executing the Minister and all Muggleborn officials on the Wizengamot, Voldemort declares himself the Magic King of Great Britain. He sets out immediately to reorganize and reform the Ministry to better suit his desires of the perfect society.
He begins segregating the Magical World, imposing distinct classes based on magical/blood purity. All Muggleborns are immediately removed from Hogwarts and get transferred to a new school called Hogpen School of Integrated Magical Learning, which the primary purpose was teaching the children their places in magical society. It is made illegal and punishable by death for a Muggleborn to use or even touch a wand. It's illegal for them to own any magical artifacts or possess them outside their designated workplaces. Older and fully trained Muggleborns (from before the Great Reformation) are hunted viciously within Great Britain by a new Auror subdivision called Snatchers by the public. The Muggleborns' wands are snapped and they get imprisoned in Azkaban for ten years if they surrender peacefully. If they don't surrender, they get executed on the spot. The smarter Muggleborns escaped Great Britain before Voldemort consolidated his power. Now it is illegal for Muggleborns to travel abroad, under any circumstance.
Aurors only police Pureblood crimes and ignore injustices against the Muggleborns, unless the Muggleborns 'caused' it for which the punishment is usually very harsh. But while Wizards are generally elevated to higher social status, certain Dark Creatures are allowed free reign against Muggles in Voldemort's gratitude for services rendered, creatures like vampires, Dementors, and giants.
Naturally, many Muggleborns formed underground resistance cells, each trying to discreetly topple Voldemort's new ministry and his 'Dark Assembly' (the Wizengamot's replacement).However, their successes are miniscule at best and accomplish next to nothing, causing many Muggleborns to start losing hope as the years pass and the chances of returning things to the way they were grow ever fainter.
1980
When the prophecy of Voldemort's defeat was made, he immediately sent out assassins to find and capture the ones most compatible with the prophecy's wording. The Longbottoms and Potters each fought back to protect their babies. The Longbottoms were incapacitated and Neville taken. But the Potters were able to fend off the Death Eaters long enough for Remus and Sirius to arrive before they were overwhelmed and killed.
Caught by surprise by Remus and Sirius's flanking attack, the Death Eaters were quickly killed and the Marauders took infant Harry and were able to slip around the magical security forces and flee Great Britain before word could reach Voldemort. When it does, Voldemort sends his most skilled and trusted hunters after them to find and capture them, bringing them before him at all costs.
Remus and Sirius raise Harry on the run, constantly evading Voldemort's hunters and other mercenaries who are after the large bounties on their heads. They journey throughout the world, Harry learning many different ways of doing magic from many different schools and philosophies.
1985-1995
Unsatisfied with ruling just Britain, Voldemort invades Ireland. Ireland becomes the testing ground of several strategies for how to conquer a country. They first used an army of drafted Muggleborns as cannon-fodder to draw out the Irish defenses and observe their magical skills. Next came the assassins, targeting the government officials. After two months, six large-scale battles, and over 20 assassinations, the Irish surrendered unconditionally to Voldemort.
Voldemort next turned his attention to Portugal and Spain, instigating civil unrest in the countries by provoking the radicals. War quickly broke out between them and from within, making life on the peninsula extremely dangerous for magical and Muggle alike. Less than a year later, Voldemort's new army came sweeping through and conquered both in less than a week's time with relative ease.
He forces the Ministries and militaries of Ireland, Portugal, and Spain to all swear absolute loyalty and obedience towards him. Then he sends 'representatives' to evaluate the 'economy' of the countries. If they don't match Britain's new social structure exactly, the representatives force improvements on the laws and customs, completely disregarding the native ones.
Rather than be taken like the rest, France calls an emergency session of the ICW to try and stop Voldemort. However, Voldemort is able to dodge the ICW because he hasn't broken any international laws…yet. Furious and unwilling to fall so easily into Voldemort's growing empire, France launches a surprise attack on Britain. True war finally erupts as the new Magical British Empire all launch simultaneous attacks on France in retaliation.
The rest of Europe just waits and watches from sidelines, believing the fight wasn't theirs and they'd be left alone if they didn't interfere. Not only that, but several of Voldemort's agents are already at work within other countries, causing and spreading civil unrest and wars and keeping the countries focused on themselves and not the larger threat.
1996
Harry finally returns to Europe via the Mediterranean, landing in southern France. He desired to see his birthplace and the country that his parents had loved so deeply. What he wasn't expecting was to get caught up in the new Magic War.