Will I need any special licensing for putting any real locations like the Highway of Death and real underground bases and desert regions where there were made up experiments and hybrid villains during Operation Desert Storm? Will this be an issue for those who fought in the Gulf War? What if I included some of the Iraqi Republican Guards as bad guys? Will anyone care?
And during some secret covert operations to find secret weapons in Russia in the 60's, is it better to make up those secret locations? Or ok to use real places like the Russian Temperate rainforests, East Berlin? Or the Ural Mountains?
*Cracks knuckles*
The politcal elements first:
I write books set in Northern Ireland, some of which make reference to the Troubles (albeit in a roundabout fashion; these are SF and fantasy, not political in nature), and the wider political arena that is NI. People invested in anything NI are very, very quick to pull me up when I get anything wrong (which, when writing in a politically charged arena, has a wide definition), but are almost always generous in understanding that, as an invested person (ie I'm from NI, and do belong to one of the traditions within the country - it's nearly impossible not to have an allegiance - albeit I'm very moderate), I do have my personal take on the history and definitions that form NI. (I do try to show a balance of the communities in my books but one, in particular, is very much based in the Unionist community - but it's the less political of the two released to date)
What's important, then:
A good understanding and sympathy for the underlying history and cultures of those impacted by your story. People will care, very much. And they will be knowledgeable. It's up to you where you take your bad guys from but they need to feel real, to have motivations and those motivations will be challenged, so be very sure of your ground.
(*musical interlude* This is why Spandau Ballet are (often/largely/insert whatever qualitative needed here) derided in Belfast for their song, Through the Barricades, where Simple Minds play Belfast Child to huge cheers - one was a weak take on the Troubles (in my opinion, I'm sure there are some people who like it) and their nuances which was made pop-py, the other was a better researched song which drew on a very well known Belfast ballad (She Moved through the fair, for anyone interested. It came down to respect and not making the NI people feeling like they were lining pockets of someone else by being cheap entertainment. It helped for this, then, that Simple Minds were from Scotland and familiar with sectarian conflict more than a band from London, perhaps)
In terms of the landscape
People are more generous on this one. I open one of my books at a Waterfall that has a slightly different layout than the one I describe (I needed two paths to join in a horseshoe where, in reality, one continues up to a car park), and that one hasn't had anyone pulling me up - even people very familiar with the place. The feel is right and there is room for literary interpretation.
However, I have one due for publication next year that is set in quite a well known place, Glenveagh in Donegal. I did umh and ahh about naming the place, because I don't know the layout intimately, but decided it was too clearly Glenveagh not to name (and I draw on some of the real history of the estate, too) - it's a very unusual place. That being the case, I had to bite the bullet (life is hard) and go to Donegal for a long weekend to go back and revisit the estate. I took photos, recorded sounds, walked the paths my characters would and, generally, nailed down a lot of the inaccuracies. For 95% of readers, it won't matter. For those who know the place, it could pull them out of the story if something feels very wrong. More importantly, for me, I'm confident in what I'm writing, and that helps things a lot.
Google maps are your friend, especially StreetView. For me, I feel less confident writing about places I don't know and I'd try to visit if I could.
Good luck with it!