Some events are far-off historical events. The most you risk if you write about them without doing the proper research is making a fool of yourself.

Other events are still within living memory. Some of your readers might have lived the event. @SaraCosta says in the comment that not doing research is a sign that "the writer has very little respect for their chosen period / event". Well, there would be living people whom you'd be disrespecting.

One particular way in which you could show disrespect is believing yourself to be exaggerating an event, when in fact you're falling drastically short. I always have a nervous twitch watching Casablanca, when they talk of Laszlo having escaped the Concentration Camps. I think of a concentration camp, I see this (warning graphic):

(source)

Only, of course, when Casablanca was filmed, they didn't know yet. At least, the film-makers didn't.

The issue with believing yourself to be exaggerating an event, when in fact you're falling drastically short, the way you're being disrespectful, is you're underestimating the magnitude of the event. You're underestimating how big it was, how horrifying, how inescapable. You're telling people that their experience is not as big as they know it to have been. That can strike deep.

Also, if an event is still within living memory, it isn't too hard to do the research. You can find accounts and testimonies - written, or on youtube. Because research is easy, it follows that you didn't bother to do the research - you thought it "not worthy of your time", "not sufficiently important". That is how people would see it, and this too they would find offensive.

In general, avoid writing about things you don't know

You are right to have misgivings about writing on a topic you haven't researched. There are a lot of risks involved in doing this. You risk offending people by accident, you risk misrepresenting real people in your work and you risk being called a lazy writer for not doing your research.

Know your topic

With most topics it is nearly impossible to write about it well if you don't know what you are talking about. To write a good story set in London you need to know what London is like. Either you have lived there and know if from experience, or you do extensive research on the culture, layout, transport, architecture and climate. To not do this would open yourself up to poor reviews where readers correct all your mistakes. The same rules apply to historical settings.

Avoid giving details that may be wrong

If you feel that this is the only setting in which your story could work, then you should do the research. If you don't want to then avoid detailing the setting anymore than necessary. It is possible to write a story with a backdrop of a historical setting without giving details of it.

Many stories use the World Wars as a backdrop for the story. The Chronicles of Narnia is set during World War II but doesn't go into detail about the war itself. (Not that I'm suggesting C.S. Lewis didn't do his research) You can do a similar thing if you focus your story on a smaller scale, focus on the characters and the narrative rather than the setting.

Add a disclaimer

This work of fiction is for entertainment purposes only. Any misrepresentation of actual events is unintentional.

This won't stop people being offended, but may prevent the backlash.

I've given some advice on how to get away with writing without research, but my real message is: Do the research. Your writing will be better for it and you might learn a few things along the way that you would like to include.

Just don't.

You have a good ten thousand years of (semi) recorded history to choose from, in what is now hundreds of countries and multiple continents. There are many places and times you can pick that most people would know nothing about and you can get away with making stuff up.

Don't pick an event that has deep meaning for a very large number of people and is studied and commemorated by a good subset of them. If you're lucky, the worst that will happen is that people will think you're disrespectful.

Remember, a fair number of people out there believe the Holocaust never happened (or was a fraction of what it was in reality) and so they make up stories to downplay it. It doesn't matter if you think you're going to make it seem worse, the fact is that you'll be making up stories (and I don't mean ordinary fiction) and calling them history, and that's not okay.

Also, if you don't do the research, how do you know if your version is "worse?" Chances are, as other answers have pointed out, that you can't fathom the horrors of the actual Holocaust. I doubt anyone can without having lived it or learned about it from people who have.

As for other historical events, it depends. For events without a lot of attached emotion, if you get some things wrong, most people won't notice and some people will and will laugh at you. If you can live with that, then go for it.

Every author will mess up here and there and nearly every author will also make choices they know are wrong. I just posted a question where I am using a song written in a language that didn't even come into existence until a good 400 years after my setting.

But that's very different from deciding to be ignorant. Why would you want to use a large important event so recent that living people were actually there, as a...backdrop? tragic setting? life lesson? I can't even fathom what makes you think this is a good idea.

If you don't want to do the research --and I sympathize with that --then you are not writing ABOUT a historical event, you are writing INSPIRED by a historical event. In that case, you and your readers would be best served by you presenting your story consistent with what it really is. So don't write about the Holocaust in Nazi Germany, write about "The Troubles" in fascist Ruritania. That way you're making no promises of historical accuracy, and can freely imagine your own scenario, taking as much or as little inspiration from history as you want.

If you are writing about history, even if fictionalized, then you'll want to make all the details that aren't specific to your actual story and narrative as accurate as you can. The stakes and the scrutiny are greatly raised in the case of something like the Holocaust, still on the edges of living memory, affecting millions of people, horrible at a grand scale, and inextricably tied to politics, race, religion, and any number of other hot-button issues. Not doing your due diligence here would quite rightly expose you to charges of cheap exploitation of a terrible tragedy.

As a side note, as someone who personally does NOT enjoy the research, I've learned it really is not avoidable. Even when writing fantasy, you need to make the world seem real, and that requires work, whether that is creative world-building, real-world research, or a combination of the two.

If you want to write HISTORICAL fiction. The history is a prerequisite. I absolutely agree with all of the comments about causing offense and being just respectful (especially given the magnitude and the cultural/ Historical/ emotional significance of the Holocaust). Additionally, from a purely writing perspective, you need to truly understand a place and time period to be able to bring emotional reality to it. You need to assume that many of your readers will actually know something about the topic. Ask yourself what your intended audience is. Are you really hoping to be read by people dumb enough not to notice that you don't know what you are talking about??? Probably not.

If you don't want to do the historical research, consider writing an entirely fictitious story that has a metaphorical connection to the historical period of your choice. There are many ways of doing this. I am pretty sure that J.K. Rowling did not start writing Harry Potter thinking "I have a great extended metaphor for Fascism." However, that historical and ideological context certainly provided fuel for her storytelling. Arthur Miller's "The Crucible" employs the more complex approach of intentionally applying this technique in reverse, using the Salem Witch Trials as a metaphor for the McCarthy Hearings. If you do not want to immerse yourself in a real historical time and place, an entirely fictitious one could allow you to tap into whatever you were hoping to get from the historical setting without tying you to the facts.

Otherwise- do your research!

If you don't want to research the history directly, you may want to look into the historiography -- how the history of something is studied/understood.

Often that is why we supermoderns laugh at older works, because they made assumptions we think are silly, but by working from the common narratives of the time, yep, the "Dark Ages" were generally a bad time, instead of a poorly-documented one (well, few were available about that time for ages.)

Or a well-publicized Winner's Edit view of history ("Manifest Destiny" was taught in my elementary school as the normal way of the world -- now I realize how colonialist it is/was). Often things such as oral histories were disregarded as not "real" because they weren't the expected "formal" style.

Listening to a few podcasts (especially Tides of History and "Our Fake History"), I've learned how historians now incorporate the findings of archeologists and other non-textual documentation to understand the world.

before I go deeper, a key point: I'm assuming we ARE dealing with Facts = Facts: no denying it happened, no minimizing 6 million Jews, and about 10 million other victims.

So for the Holocaust example - how is it taught in Germany, where (to my in-researched recollection) Nazi imagery is forbidden? How is it taught in countries in Africa, who have had their own genocides, but perhaps little contact with most European history? Was it understood differently?

I was profoundly influenced by the book Guns, Germs, and Steel , in which the fact that Europe/Asia is mostly an east-west spreading land-mass, while Africa and the Americas are mostly north-south spreading -- so the commonalities of terrain influenced how abilities and information were shared, creating feedback loops.... What sort of feedback loops influenced the every day European Citizen?

Many more Theories of History are available as lenses to use for research. You don't need to research for fiction the same way you do for a History Test, but using these various ways of thinking about research can help give you insights into how you view your world and the world you're focused on, and thus can inspire some characters/scenarios for your book.

These theories influence a lot of subgenres: time-travel to kill Hitler? Great Man Theory. Alt-history where the Third Reich expands only so far, and America ignores it? Perhaps it would implode in a societal collapse as it destroyed some of its greatest strengths. Writing about the daily life at start of the Reich -- how did they get from originating universities to this? History of Mentalities. Perhaps it's an outgrowth of the Information Revolution which started earlier than many think...

Yes, these links are all Wikipedia -- that's because they're great starting points before deciding how to go deeper. But great fiction isn't just plot and details, but thinking about how the characters think, and how the society thinks, and whether those are in synch or opposition. So research isn't just a chore, or something done to appease nitpickers, but ways of understanding conflict and character in very deep ways. (This is also why fiction-reading leads to great empathy -- a good writer can help you understand why someone would make decisions that might seem impossible.)

Good luck! This book sounds hard, but it could be great!

I'm annoyed when an author gets the streets wrong in a city I know (Commonwealth Avenue is not in Cambridge) or elementary physics wrong (16 feet per second per second isn't the same as 16 feet per second.)

Real examples, but I've forgotten the titles of the novels.

Mischaracterizing the holocaust would be much more than annoying.

Any writer who doesn't want school children to point out errors in his work should do the necessary historical research.

Isaac Asimov once wrote an introduction to a book by L. Sprague de Camp describing de Camp's research for his historical works. But sometimes de Camp's research failed him.

The protagonist of Lest Darkness Fall (1939) is transported to Rome in the 530s. He asks for directions from the Pantheon to the Forum and and is told to turn left where he should turn right. He arrives at the Forum anyway and sees that columns have been removed from the pagan temples. As far as I can tell from my historical reading most or all of the Forum temples still had their columns for centuries afterward. There is another scene where the standards of the Roman army are described as having the inscription "S.P.Q.R.", which many people believe they did, even though there is no evidence that they ever did, let alone in the 530s.

The Lindsay Davis novel The Silver Pigs (1989) has Roman "detective" Marcus Didius Falco investigate a conspiracy in AD 70. There is a scene set at a imperial function in Nero's Golden House, but it is my impression that Vespasian never used the Golden House, in order to appear humble. One scene is set in the vestibule with the colossal statue of Nero. The vestibule is described as a room with a roof, but archaeologists usually think the vestibule was a open air courtyard or even a recess in the palace facade.

P.C. Wren's Beau Geste (1924) gives a rather accurate impression of life in the French Foreign Legion, but has a number of historical inaccuracies. One scene establishes the date as after the death of Queen Victoria on 22 January 1901. In another scene characters reach Agades before the official first European visitors, the French mission of 1906, putting the fictional date sometime in 1901-1906. The French actually annexed Agades in 1900.

But Heinrich Barth reached Agades in October 1850.

Today a memorial tablet honours him as the first European to have ever entered the city.

One of the problems with locating the fictional Fort Zinderneuf is that it is said to have been established in the Air country, years before the French reached Agades. But Agades was the capital of Air for centuries. So Fort Zinderneuf has to be somewhere in the Air country far enough from Agades that the French would build a fort there years before they annexed Agades, among other requirements.

Another historical inaccuracy is the Geste brothers participating in an expedition and battle against Tauregs with an entire French brigade, which was far larger than any French expedition into the Sahara.

The sequel, Beau Sabreur, happens at an inconsistent date. German agents plot to drive the French out of the Sahara, and mention Wilhelm II's visit to Jerusalem when a great breech was made in the city wall for him to enter. But actually the breech being made in the city walls is an urban legend.

So the date of Beau Sabreur should be between Wilhelm II's visit to Jerusalem in 1898 and the final German defeat in WWI in 1918. But an American women visiting the Sahara has romantic notions about desert sheiks from movies she has seen, and as far as I know the first romantic movies about desert sheiks were The Sheik (1921) and The Son of the Sheik (1926).

But Beau Sabreur clearly ends just a few years after Beau Geste, and thus probably before 1910. So it has a very inconsistent date.

On the other hand, as far as I can tell one doesn't have to do any historical research at all, or can totally ignore your historical research, if you write for movies and TV. At least that often seems the case when watching movies and TV shows when I know anything at all about the historical periods.

For example, I haven't seen Hostiles (2017) but it is said to be a good movie. But this synopsis seems to be historically implausible.

In 1892, after nearly two decades of fighting the Cheyenne, the Apache, and the Comanche natives, the United States Cavalry Captain and war hero, Joseph Blocker, is ordered to escort the ailing Cheyenne chief, Yellow Hawk--his most despised enemy--to his ancestral home in Montana's Valley of the Bears. Nauseated with a baleful anger, Joseph's unwelcome final assignment in the feral American landscape is further complicated, when the widowed settler, Rosalie Quaid, is taken in by the band of soldiers, as aggressive packs of marauding Comanches who are still on the warpath, are thirsty for blood. In a territory crawling with hostiles, can the seasoned Captain do his duty one last time?
Written by Nick Riganas

https://www.imdb.com/title/tt5478478/2

And anyone with a basic knowledge of real life Indian Wars history knows there weren't any hostile Comanches roaming the plains in 1892.

And it seems to me it would have been really easy for the scriptwriter to select a fictional year - 1872, for example - when hostile Comanche warriors were a danger.

The Fantasy Island episode "My Fair Pharaoh/The Power" (10 May 1980) featured a historical character portrayed by an actor four times as old as the character ever lived to be. https://www.imdb.com/title/tt0577765/3

And examples of errors in television can be found even in allegedly non fictional TV programs. For example, the Bone Detectives episode "The Warlord of Bamburgh Castle" (24 March 2008), was about Edwin (killed AD 633), the first Christian king of Northumbria in Britain. And Edwin probably did have a stronghold at Bamburgh.

https://www.imdb.com/title/tt1192189/?ref_=ttep_ep124

So filming scenes at Bamburgh Castles was a good idea. Except that they forgot to mention that the present stone castle there was built centuries after Edwin's time and rebuilt about 1900.

And they said that Edwin's enemies Penda and Cadwallon were his enemies because they were pagans and Edwin converted to Christianity. Penda, king of Mercia, was a pagan, but members of his family converted to Christianity and Penda had political reasons to be Edwin's enemy.

Cadwallon, king of Gwynedd and probably king of the Britons, was a Christian from a family which had been Christian for centuries and produced a number of British saints, including his own son Cadwallader the Blessed. Cadwallon attacked Edwin because Edwin had invaded Gwynedd and driven Cadwallon into exile in Ireland.

I wonder what Mr. Evan Vaughn Anwyl of Tywyn thought if he watched that episode. Why should he care? Because he is probably the present day heir of Cadwallon, and since a legend claimed that Cadwallon married Penda's sister, possibly also the heir of Penda.

https://en.wikipedia.org/wiki/Anwyl_of_Tywyn_family5

The first historical error I ever noticed was when I was in an elementary school which I left when I was eleven. The class watched a sort of television documentary on the Little Bighorn. It mentioned that Custer sent a detachment under Captain Benteen one way and a detachment under major Reno another way and rode on with the rest of his men in a third direction. So far so good. But then it said that Custer reunited with Benteen and Reno before making his last stand.

And that didn't sound correct to me. So I checked out a couple of books about Custer and Custer's Last Stand from the school library and the public library and read that Reno and Benteen did not, repeat not, reunite with Custer before Custer's Last Stand, which is why most of their men survived.

Being an introvert, I didn't bother to tell anyone. But any kid who was more extroverted than I was might have complained to the teacher about that error, which could have resulted in some humiliation for the creators of the documentary.

So any writer of fiction or non fiction who doesn't want to be humiliated by school children pointing out his errors should do the necessary historical, scientific, geographic, etc. research.

In contrast to other answers, I have to say that research is not necessarily required. This is entirely dependent on your intended readership.

If you're writing a bodice-ripper set in King Arthur's Court, well, research won't help you much and may well get in the way. Your audience probably doesn't know and doesn't care that life in them times was nasty, brutal, and short, and that chivalry was widely admired and just as widely ignored. Inconsequential details like universal fleas and lice will just get in the way of the story. The charming custom of bathing once a year probably won't help with modern readers, either - at least not the sort who read bodice-rippers.

In fact, what you need to do in this case is no research at all on what life was like back then, but rather concentrate on the knowing the preconceptions of your audience.

What you need to do above all else is to learn what the audience will and will not accept. Accuracy is entirely optional. Acceptable verisimilitude is not.

Do the research.

A good point to start from:
https://www.yadvashem.org/