I have story ideas that involve civil wars or revolutions happening while a character is travelling. I was wondering what would be the advantages and disadvantages of setting such a story in a made up country, compared to a real one.
Amadeus' answer very nicely shows the advantages is using a fictional country, so I'll focus on one trap that is easy to fall into.
Call it Ruritania or CommieLand (obligatory TvTropes warning) - a set of stereotypes of a whole diverse region of the world bunched together into one fictional country. You can find a lot of examples of this American action/thriller films (especially, but not exlusively, B movies). You get your mobsters from generic Balkan countries, your drug smugglers from generic South American countries, your tribal warlords from generic African countries, etc.
This is, of course, an easy way to avoid the unpleasant consequences of naming existing states, as mentioned by Amadeus. But it can also be alienating and verging on offensive for audiences from the Balkans, South America or Africa, who do not consider their own country just one in a mass of unrecognizable peoples.
The advantages are not losing a large proportion of your audience, and not being accused of being a racist, a liar, a hater, a bigot, an ignorant writer, etc.
If you use a real country, there will be people both attached to that country, and opposed to that country. There are real facts about that country and its history. There will be vested interests there; what you say about the real country and its previous politicians and celebrities will be subject to expert scrutiny and criticism. People may grow to literally hate you for what you have written about "their" country.
If you use a fictional country, and make it different enough from any real country, you can sidestep all these issues. (You can't just change the name from "The Soviet Union" to "The Marxist Union" and leave everything else exactly the same; everyone will see through that.)
You liberate yourself to create a new history, whatever the story calls for. A new culture and traditions, perhaps a new religion or lack thereof. New politics, or a new dictatorship.
If you want a country in the same geographic area with a similar culture, you can even change history: for example, The "United States of America" never existed; the colonists lost the American Revolution. But in 1788, when King George III went literally insane, he was assassinated, and in the ensuing chaos a second American revolution succeeded, but this time an American monarchy instead of a Democracy. And by the time George IV was secure on his throne; the American King had consolidated his armies and territory, and it was too late for the UK to do anything about the Americas; George IV had domestic issues and enemies to worry about.
You have greater freedom, complete freedom, with a fictional country. It takes a little more work and you can't be lazy and just crib from reality, but that's the point: Write Fiction. Use your imagination. And avoid all the baggage from reality and real emotions about real places.
Every revolution is different. Every civil war is different. They are different in why they are fought, they are different in how they are fought, they are different in who is fighting. (To clarify, I do not mean the obvious "who" as in "the English" or "the French". "Who" can mean different classes, different tribes, it can be different noble families fighting on the back of peasants who have little interest in who wins, just so long as the fighting stops. Compare, for instance, the War of the Roses to the Russian Revolution.)
It can be that you want to say something specific about a particular struggle, about a particular location and period. Or it can be that you are writing a story that needs some form of civil unrest as a story element, but the exact details are unimportant. Those are two distinct cases, so I will review them separately.
You want to say something about a specific struggle
Let's say you want to talk about the French Revolution. You can talk explicitly about France, or you can use an invented country as a metaphor for what you want to say.
Talking directly about France, what you're saying gains a measure of "this is true, this is what happened, this is how it was". It might not be completely true in all it's particular details, but it is true in spirit. Take Les Miserables as an example (yes, I know its events are set several decades after the French Revolution; it's just a famous example) - the particular boy named Gavroche might never have lived, but in the streets of Paris there were many similar "Gavroches".
The strength of such a presentation is also its weakness. You bind your story to a particular place and time, it remains bound to that frame. If you wished to take the side of the Royalists in the French revolution, it would be hard for the reader to untangle themselves from their already existing view of the French Revolution giving us such ideals as Liberty and Equality. (A concern more pertinent the closer the event you're describing is to our times, that is the more the issue is one of politics rather than history).
At the same time, it's all too easy for a piece about a certain period to be read as being about that period only - without any hint to modern times that you might want there. France is only far-away, in-the-past, France, but "made-up-land" easily becomes "every-land" and "my-land".
Your interest is not in any specific struggle, but in "a struggle"
As @Amadeus points out, if you write about a real struggle, you have to do the research about it, and you are bound by it - it might not go where your plot would like it to go. That is one consideration for making up your own land.
Concerns about readers having pre-existing opinions about the particular struggle, which might not mesh with your story, are all the more pertinent, since in this case the particular conflict isn't even interesting to you.
But there is an advantage too: if your character arrives in Paris in early 1789, you don't need to give your reader all the cultural background of what's going on - they already know at least the general framework of what's going on. The stage has been already set for you, so to speak. In fact, you can create dramatic irony (e.g. "The Bastille would stand forever") and you can create anticipation (the reader eager to see the storming of the Bastille, while the MC has no awareness anything like this is going to happen).
Now, with those considerations in hand, you can see what serves your story best.
Some of the advantages is that you can tackle a real world conflict with a fictionalized culture without a lot of the stress of the situation. Even if it's unlikely that you would have a readership in the real world conflict, keep in mind that the situation in a civil war is rarely as cut and dry down the middle. Even the U.S. Civil War had a lot of politics beyond slavery behind it and many southern soldiers were not slave owners (General Robert E. Lee was actually an abolitionist and hated slavery, but was a patriot to the state government Virginia over the Federal Government or the United States. Lincoln had the misfortune of offering Union Commander to Lee the day after Virginia succeeded from the Union). Portraying this in a fictional nation allows you to tackle the politics of both sides.
The disadvantage is it's obvious you're dancing around the real world issues. Writers have a wealth of history to inspire their civil war's history, and this tends to mean that they often correlate to the real deal in some degree. This is especially true in Scifi and Space Operas where it's "a historical war with Space Ships". Star Wars, for example was largely WWII naval and air battle re-enactments (George Lucas went so far as to listen to radio chatter from actual WWII battles). Firefly is from the point of view of a Southern Soldier in the aftermath of the Space!U.S. Civil, though the slavery issue wasn't a driving factor (Our hero justifies stealing money off of a fellow bar patron because the victim was a slaver and the money was stolen off his profits for not paying his labor), the extent of government control over people was a major theme. Star Trek Deep Space 9 is sort of a Cold War leading to the naval aspects of World War II (to the point that Sinatra style big band lounge music enters the pop culture of the period).
Because of these parallels it may defeat the point of making a fictional country (though it does remove the conflict of blaming a particular country as the aggressor. One of the reasons why Torah Torah Torah is still considered the definitive Pearl Harbor movie is that U.S. and Japanese film studios worked closely together to ensure that both sides were portrayed accurately and that neither was disparaged. Compare to the late 90s Pearl Harbor, which depicted the Japanese committing war crimes they did not committ vs. Torah Torah Torah, which had a glaring detail of misquoting Yamamoto in the closing as it's most glaring inaccuracy (Yamaoto never said the final line in the movie, but his sentiments about the coming war were pretty much in the same line).
And then we get to the bizarre, where there are some occasions where the people who you oppose obviously see themselves as the side you oppose, and do not care... they love the romance of their struggle and are happy for any acknowledgement of the matter, especially if you are fair in your portrayal of the matter. Although I have no actual examples, I submit the Airport scene in the film Argo, where one of the hostages posing as an advance scout for a U.S. scifi film to escape Iran is asked by the Iranian government details about the film. He improvises and basically tells about the rebellion against an unpopular king installed by an evil empire and the struggles of the people against the regime. It's pretty much the situation in Iran from the point of view of the Iranians and the guards are so geeked out that Hollywood is making a film about it, they let the whole crew go without any hassle in exchange for concept art. Although this is mostly humor in the very tense scene, the real life incident did have the Iranian government provide helpful support to the cover of the film scouts for much the same reasons (the west is showing our side in the next Star Wars!). And this kind of surprising support is actually fairly common (TVTropes has a whole series of Articles titled Mexicans Love Speedy Gonzales which discusses favorable attitudes to foreign works that depict their culture in a negative light. It's named for the outrage Mexicans felt when Warner Brothers tried to limit the cartoon character's exposure on American Television in the 90s out of fears they offended the Mexicans... They wanted more of Speedy, not less).
To provide advantages of using existing countries:
You have to do fewer introductions and explanations.
People have an idea (however vague) of what kind of a political system is in place in a certain country, what the make-up of its population is, which conflicts lie at its heart, which defining past conflicts it may have had.
Same applies to the scenery or culture of the country. You do not have to make it believable. It already exists, as long as you stick to the facts (or clichés, if you must) of a country, people will take whatever they know already to supplement your sketchy picture of the country.
You can get into the action, the things that are unique to your story, much more quickly.
Also, you can leverage the personal relationships of your readers to certain countries. E.g. if you write a story for Germans, and the revolution happens directly below it in Switzerland, you immediately get impact on your readers. They may recall vacations they had there, they may even have friends or relatives there, they may be shocked to think that something like this may be going on right at their doorstep.
You also have a more rigid framework for your story. Certain things just don't happen easily in certain countries. So if you pick that country, you can intrigue your readers by showing them how a seemingly impossible thing can slowly, small change by small change, happen in a place they wouldn't expect it to happen in.
And things happening in one country have an effect on the surrounding ones. If the US suddenly went down the drain, the entire world economy would change abruptly, the military power balance would change. If Liechtenstein went under, it would probably cost a few people in Switzerland dearly because of their close economic and infrastructural ties, but beyond that, most of the world would probably hardly blink.
Also don't underestimate the knock-on-effects: Using real countries in a series of stories means that a revolution has consequences for the entire world. There won't be any more stories set in the Kingdom of France once the French Revolution happens.
On the other hand, if you make up your own country, not only do you have to "waste" a lot of time just establishing what this place is, and how it looks during its heyday, just to then tear it down, but you also have to convince the reader why they should care, you have to establish relationships with the surrounding countries etc. If you just make up a few countries as "redshirts" to be "killed off", readers might not miss those countries. They weren't there before, they're not there (or at least relevant) afterwards.
Also, it might be boring to read. If you make up a country with the objective of tearing it down via revolution, you'll probably give it a structure that facilitates that. Which means attentive readers will expect it to go down, and won't be surprised or intrigued. They might just go "yup, they had it coming".
Oh, and don't forget that you end up being "genre" if you make up your own country. It is common in Scifi and utopic/dystopic storytelling to make up new worlds or countries, but certain audiences see that as "lesser" storytelling. It all depends on what kind of a text you are going for, and what purpose you are writing it for.
Create a fictional country if there are no existing ones that meet your needs. Or if you need to change things enough that it would be confusing or off putting to place your characters there.
If your story is set, for example, with the Spanish Civil War as the backdrop, then you would need to allow the timeline to unfold as it actually did. Unless you're doing an alternate Earth, but that's an entirely different issue. So you shouldn't change the major players in Spain and elsewhere, or change the dates, but you could still place fictional characters there.
If you'd like to show a major event (like a civil war or revolution) and the country that works for your story didn't have such an event, then don't use that country (unless you're placing the story in the future). Don't write a revolution in modern-day Japan.
Whether you accept the constraints of a real setting, or decide to completely make your country up, is your choice as an author.
Three main advantages:
You won't have to actually research that country... If you set the story in Iraq, there is a lot of history and politics that your readers are already aware of, and your fictional iraq must share much of the same history as the iraq that people know.
You won't risk offending the actual country. If you write about a real country like China, India, Saudi Arabia, etc. etc., many of them can get very sensitive about your portrayal of their country.
You can have a lot more artistic liberty about your fictional country.
There is a key disadvantage....
- You risk looking like a mega racist. Now you making broad stroke assumptions about an entire continent...