Let's assume voldemort wins (and for good measure he still has the diadem horcrux) what would his rule be like. I assume:

Immediately muggleborns would either be killed or worked to death. Some New muggleborns are quickly captured and killed once their name is on the Book of Admittance. Though not every wizards name is put on the register so some may fly under the radar.

Voldemort reveals himself at this point, making official what before people had only suspected. Because he has no need to hide in the shadows and to scare the population into submission.

The new regime heavily favors purebloods, muggleborns are either killed or enslaved. Half-bloods are looked down upon and only barely tolerated I imagine they would be relegated to second class citizens.

His government would prioritize power and domination, potentially leading to economic instability and social unrest. The use of dark magic and fear tactics to maintain control would create an atmosphere of dread and secrecy.

Keeping a population under force of arms is difficult. Nations like North Korea are able to do it because they are completely isolated and the people are too focused on not starving to death to rebel. I imagine it would be a lot harder with magicals.

Im unsure if Voldemort would try to launch attacks on other nations. Even he would recognize trying to take on all of europe would be a very tricky task. With his one horcrux he can't die, but his followers can and it only takes one killing curse for voldemort to spend years looking for a new body. The UK would probably end up a pariah state, too focused on internal matters to focus on waging any kind of offensive wars.

His government would also engage in killing muggles, but in very small numbers. I know in the cursed child they bribe the muggle pm to look the other way, presumably so he doesn't tell other leaders who then tell other magical leaders.

I discussed this on reddit once, and it was suggested that Muggleborns may work for Voldemort. I disagree, not only would it take huge balls for a muggleborn to even approach the new government, Voldemort and the death eaters have made it clear, they dont want Muggleborns.

 

Honestly I think it would not be too dissimilar to what we see in 1991 - 1993. Just without Muggleborns. But they're such a tiny proportion of the population that you probably wouldn't even notice the difference.

It would be less democratic and more aristocratic, favouring the purebloods. But even in 1991 Britain is not super democratic - a single election every 7 years to elect what appears to be a temporary dictator - so that's not a huge change either.

And I doubt the international community would care. Durmstrang doesn't accept Muggleborns and no one lifts a finger about that. Clearly anti-Muggleborn feeling is quite common internationally - potentially even the norm, with Britain being an unusually liberal outlier.

I also don't think that magical states go to war. They don't have armies and there's a limit to how much you can war within the Statute of Secrecy (which Voldemort observes and respects). I think over time Voldemort would just extend his influence through the ICW in much the same way he took over Britain: bringing people to his side through a mixture of promises and fear, with the occasional murder to remove an incorruptible obstacle.

 

I don’t think the only significant differences can be summed up to “No muggleborns + more aristocratic” though. It does seem like the society genuinely became more totalitarian and dystopian in nature during Voldemort’s short reign. For instance, there is the example of the Carrows forcing students to use the cruciatus curse on each other.

That said, it could be argued that Hogwarts is not unfamiliar with the concept of torture, since apparently students were whipped and hanged by chains in the past (if we are to believe Filch). So it’s plausible that this isn’t necessarily that crazy by contemporary wizarding norms, especially as this happened during a time of conflict.

Still, one aspect that would change is the climate created by the erosion of social and legal norms brought about by Voldemort’s capricious and sadistic behavior. He was more than willing to burn down Hogwarts and everyone in it to achieve his aims, so it’s not unrealistic to think that the average citizen would live with the constant fear that he might snap and kill their family, or something like that. Even his supporters must constantly fear the consequences of failure.

It doesn’t seem like this situation would improve much either once Voldemort has achieved total power and ended all rebellion. Sadism is just a core feature of his personality.

 

Especially since his definition of "total power," would probably be very fluid. He would always find something he doesn't have and crave it.

 

It would certainly be something to see Voldemort address the ICW. His appearance alone would probably terrify the other members.

Unlike what fanon thinks I don’t see Voldemort waging a war like Grindelwald did to conquer muggles. Voldemort seems completely okay with wizards living in the shadows. He’d probably work to make the Statute even more strict. Complete cut off from the muggle world.

Maybe he will finally live out his dream of teaching DADA!

 

In the cursed child, we know that death eaters are bribing the muggle prime minister with gold. into silence over the various atrocities being committed by Death Eaters and other wizard misfits, such as blowing up bridges to see how many Muggles they could kill. Presumably, the death eaters are scared of the ICW.

 

It’s hard for me to believe the government that is hinted at in DH would be sustainable for long. I think Voldemort and the Death Eaters would probably end up being pretty bad at keeping the country running, and the basic fundamentals of a functioning society would start to break down. Leading naturally to widespread suffering. Possibly revolt, violent suppression of that revolt, and so on.

 

Voldemort probably wouldn't rule directly, I doubt he cares about things like taxes and tariffs. He would probably just give positions to his most loyal followers.

But his followers would probably put their own selfish needs above the rest of the population. I imagine the common person would become dissatisfied with a lot of the news laws that reeked of self indulgence. After economic instability, some might get disgruntled enough to seriously think about rebelling.

Probably not a full on revolution, but low intensity guerilla warfare (like the ira, or taliban)

 

So I think there are a few things that we can reasonably infer based on the population of Wizarding Briton, and the general (albeit very biased) perspective of Harry and others about the Death Eaters.

1.) None of the Death Eaters have ever managed an enterprise with more than a handful of direct reports.

2.) Ideology matters to them more than competence.

3.) Holding aside certain members' experience of being rich due to inheritance or running small family businesses, none have any meaningful experience with modern economic theory.

As a result we can reasonably forecast the following things:

1.) Administratively, the UK would be a mess. This means that hospitals would have incredibly long wait times, empty beds would remain unfilled while UK doctors and other healthcare professionals either voted to strike or left the field/country entirely.

2.) Compounding the mess in item 1, those appointed to fix the problem would attempt to force compliance but would be too inept to make it scale up properly.

3.) The UK would see year over year double-digit inflation while other economic indicators continued to worsen and runs on limited supply essential goods would cause general panic.

TL;DR, the Death Eater takeover happened at some point in 2019 or 2020. UK DLPers, blink if this post is an accurate summary of your country post Death Eater takeover.