Including real people in works of fiction is extremely thorny from a legal standpoint.
Your question states that you are talking about organizations and politics, and not specifically naming people, but since an organization and a political system must necessarily include discussions of the people in them, I'm going to give you that perspective.
Have you ever wondered why there's always a disclaimer in front of certain books, usually somewhere on the copyright page or the inside cover, saying:
Any resemblance to real persons in this work, alive or dead, is purely coincidental.
This is why.
On the one hand, there are plenty of ways you can include real places and real events in your work without causing much fuss, because places aren't people and events aren't people. But people... are people. Especially if they're living people. That makes it different from asking if you can use the word Chicago or the Civil War in your story, because the Civil War doesn't have an identity, nor does it have feelings.
If you include any living person in your work, even if it's a satire or a caricature or anything else of that nature, you are opening yourself up to a world of problems. Particularly because you say outright that your work doesn't paint them in a very flattering light. Even if you disguise who the fictional character is supposed to represent, i.e. changing their name, it's still usually pretty obvious who you are modeling that person after. I couldn't include a pompadour-haired business tycoon who builds skyscrapers and hotels in my story and uses the word "yuge," without it being pretty obvious that the character is modeled after Donald Trump.
So, how can you do this properly? There are three things to consider.
Does your work defame the person or make false claims about them? This doesn't mean you can't insult them - you can - but you can't claim they said things they never said, committed crimes of which they are innocent, or did things they never did. That's where it edges over into potential defamation territory.
To quote this article:
Libel is the publication of a false statement that injures a person’s reputation (as opposed to slander, which covers the verbal form of defamation). The statement must be false and factual. The defamed person need not be identified by name. The writer need only use enough identifying information in creating the fictional character so that the real person is identifiable to readers.
Invasion of privacy.
Are you invading this person's privacy by including intimate details of their life in this work, or otherwise putting things on paper that they may have wanted to keep out of the public eye? When private facts that are not known to the public are included in a work, you have committed invasion of privacy, a very serious charge in most courts. Tread with care if your work includes close details of the person's life.
The right of publicity.
Are you using this person's likeness? Likeness, in legal terms, is how much your fictional character closely resembles the real person. You may recall that several celebrities have sued video game companies for including NPCs and characters who are very obviously inspired by them, and even if those suits aren't always successful or warranted, you have to be incredibly careful not to include enough information that somebody could make a likeness misappropriation claim against you.
(Source for all of this information, and further reading.)