Which historical events are different in Harry Potter, than they are in recorded history? I'm not looking for the major things that the books add in (i.e. magic), but for small things.
The generally accepted timeline is that Philosopher’s Stone is the school year 1991–2, and extrapolate outwards from there. This has been confirmed by multiple canon sources; see other sites and/or answers for details.
Given that timeline, here are some mistakes:
The days of the week are generally inconsistent.
For example, we know that Philosopher’s Stone starts on the 1st November 1981 (the day after Harry’s parents were killed). And in the first chapter it says
When Mr and Mrs Dursley woke up on the dull, grey Tuesday our story starts
But that day was actually a Sunday.
There are many similar mistakes like this in the book, where the stated day doesn’t match the actual date. A common example is the fact that 2nd September is always a Monday for each year that Harry attends Hogwarts. The days move each year, so that’s clearly impossible – in fact, it was only a Monday in 1991 and 1996 (so Stone and Prince).
The facts about the Prime Minister seem off.
In the beginning of Half-Blood Prince (so around 1996), we meet the Muggle Prime Minister. When he recalls his first meeting with the Minister for Magic, Fudge says:
“And I must say, you’re taking it a lot better than your predecessor. He tried to throw me out of the window, thought I was a hoax planned by the opposition.”
We don’t know exactly when this first meeting took place, except that it occurred before 1993 – he was in office when Sirius Black escaped from Azkaban.
It’s also worth noting that the fictional Prime Minister recalls a recent election campaign:
Naturally, he had thought that the long campaign and the strain of the election had caused him to go mad.
John Major became Prime Minister midway through a Parliament, when Michael Heseltine challenged Thatcher for leadership of the party. This was technically an election, but it would be hard to describe it as “long”. Heseltine’s challenge came in mid-November, and balloting was in December. It sounds more like this Prime Minister went through an election, and likely saw off an incumbent Government to boot.
Dudley has a PlayStation before it was ever released.
From Harry’s letter to Sirius at the beginning of Goblet of Fire:
They told him they’d have to cut his pocket money if he keeps doing it, so he got really angry and chucked his PlayStation out of the window. That’s a sort of computer thing you can play games on. Bit stupid really, now he hasn’t even got Mega-Mutilation Part Three to take his mind off things.
That would take place in summer 1994. But the original PlayStation wasn’t introduced until December of the same year, so it must have been released earlier in the fictional universe.
And there has never been a real video game called Mega-Mutilation Part Three, released in 1994 or otherwise.
If we start clutching at straws and/or moving into lesser canon material:
Bonfire Night has moved to later in the year.
In the UK, Bonfire Night is usually celebrated on 5th November. On the Tuesday when the story starts, the weather reporter says (of celebrations of Voldemort’s downfall):
Perhaps people have been celebrating Bonfire Night early – it’s not until next week, folks!
Voldemort was killed the previous day, which makes this 1st November, and a Tuesday (see above). I wouldn’t describe the following Saturday as “next week” – for me, that phrase means the following Monday or later.
In HP, King Arthur might have lived considerably later than he actually did.
According to legend, King Arthur defended Britain from Saxon invaders in the 5th and 6th centuries AD. There are also chocolate frog cards written by Rowling that have Merlin as an advisor in King Arthur’s court.
But the Slytherin welcome letter on Pottermore says:
Here’s a little-known fact that the other three houses don’t bring up much: Merlin was a Slytherin. Yes, Merlin himself, the most famous wizard in history! He learned all he knew in this very house! Do you want to follow in the footsteps of Merlin?
Since Hogwarts wasn’t founded until the 10th century AD, this seems to suggest that Arthur’s lived quite a lot later than contemporary legend.
(Alternative explanations are that the Slytherin prefect has made this up, or Merlin lived for several centuries.)
The Dursleys have a car that’s about ten years too early.
In the Order of the Phoenix film, we see their number plate quite clearly: MA06 HBH. Nominally this scene takes place in the summer of 1995.
But there are two things wrong here:
- The age identifier on that plate tells us it was issue in mid 2006. (See DVLA’s document on registration number formats, page 6)
- That’s a fifth-generation Vauxhall Astra, which wasn’t released until 2004.
Likewise in Deathly Hallows: Part 1, they’re still driving the same, out-of-time car model, but the plate has changed:
The age identifier is now “07”, meaning a mid-2007 issue date. That is still far too new.
The Death Eaters attack a London that’s way out-of-place.
In Half-Blood Prince scene with the Prime Minister, there’s a line about the destruction of the Brockdale Bridge, which must have occurred in early 1996.
This scene is reproduced in the Half-Blood Prince, but the London it depicts doesn’t match up to the supposed timeline:
We see the Gherkin in a reflection, even though it wouldn’t start construction for another four years:
They attack the Millennium Bridge, standing in for the Brockdale Bridge. But as the name implies, it wasn’t built until 2000, at the turn of the millennium.
I’m sure I could go on, but I think this gets the general gist across – there are a few inconsistencies in the books, particularly when it comes to details like days of the week, but most major historical events are in line. The movies drift more significantly, as a result of them being shot significantly after the books are set.
With the timeline firmly established by PearsonArtPhoto, we can deduce that Harry Potter and the Goblet of Fire took place in the academic year 1994/1995, with the summer holidays at the beginning of GoF being in the summer of 1994.
Thus, Dudley throws his PlayStation out of the window in the summer of 1994:
They told him they'd have to cut his pocket money if he keeps doing it, so he got really angry and chucked his PlayStation out of the window. That's a sort of computer thing you can play games on. Bit stupid really, now he hasn't even got Mega-Mutilation Part Three to take his mind off things.
Harry Potter and the Goblet of Fire - pp.27-8 - Bloomsbury - Chapter 2, The Scar
The console was released in Japan on December 3, 1994, and in North America and Europe in September 1995.
Obviously, the beginning of Harry Potter and the Half-Blood Prince refers to fictitious events in the Muggle world, such as the collapse of the "Brockdale Bridge", the giant attack that the Muggles believed was caused by a tornado, the murder of Emmeline Vance just round the corner from 10 Downing Street, a Junior Minister Herbert Chorley going mad and so on and so forth.
Perhaps more what you're looking for is the Primer Minister of Great Britain (thank you SQB) is clearly different.
But of course, it had been like this from his very first meeting with Fudge on his very first evening as Prime Minister.
He had been standing alone in this very office, savouring the triumph that was his after so many years of dreaming and scheming ...
Naturally, he had thought that the long campaign and strain of the eleciton had caused him to go mad.
'... And I must say, you're taking it a lot better than your predecessor. He tried to throw me out of the window, though I was a hoax planned by the opposition.'
Harry Potter and the Half-Blood Prince - pp.10-1 - Bloomsbury - Chapter 1, The Other Minister
We know that the events in The Other Minister take place in the summer of 1996, during which time John Major was Prime Minister. His predecessor was Margaret Thatcher, though Fudge clearly refers to his predecessor as a he.
Now, John Major took the leadership of the Conservative Party in 1990 and so became Prime Minister after Margaret Thatcher. But this was an election conducted within the Conservative Party and was not a general election, which did not take place until 1992. Now, strictly speaking, John Major did win an election and there presumably was a campaign, but to me, The Other Minister makes it sound distinctly as if the new Prime Minister had won a general election.
Also, his Predecessor Margaret Thatcher was in office from 1979, surely long before Cornelius Fudge, who apparently met with Major's predecessor, who tried to throw Fudge out of the window.
Interestingly, in the summer of 1995 (Dudley Demented (chapter one of The Order of the Phoenix)) there really was a hosepipe ban in Muggle England, which I think is quite nice.