Yikes! If you think politics are ugly today, you obviously have no idea what it was like in previous centuries. Here in Judges 9, we get a taste of dirty politics from a few millennia ago. (Once again, let me lead off with the caveat that we can't assume that God approves of any of this, with one exception that must be addressed. We'll get there.)
Having made a number of very bad decisions in his personal life, Gideon, who already had numerous wives, also gets a concubine in the city of Shechem. This woman bears him a son, which Gideon names "Abimelech", a name which means "my father is the king". This is an odd choice of names for a man who claimed that he didn't want to be king, and also for a man who was famous for fighting off pagans, when "Abimelech" is apparently a common name for local pagan kings.
So after Gideon passes on, Abimelech decides to make his move. He goes to the men of his own city and suggests that they should back him as the next leader of Israel, since he's a local boy. They agree, and he goes off to kill his 70 half-brothers, only one of which escapes. The men of Shechem crown him king. (Here's a fun bit of Bible trivia to throw at your favorite Bible-believer: ask them who the first King of Israel was. A lot of people will say, "David." Then you say, "Nope, guess again!" They think for a moment, then say, "Oh, yeah! It was Saul, right?" Then you can smugly say, "Nope, it was Abimelech, Judges chapter 9." Of course, then they might argue how technically Abimelech doesn't count, and they might be right, but you've had your fun.)
Now, the SAB laughs at the idea of talking trees, and while yes, it's absurd, it's pretty clear from the context that Jotham's story about the king of the trees is a parable; a fable-like story with a moral point. The point of the story is one that we can take to heart today, even: most people want a strong leader over their country, but the fact is that often the set of people who would make good leaders and the set of people who actually want to be leaders don't have members in common. (The side-note about alcohol is addressed here, basically that alcohol is good in moderation.)
After Jotham's speech, we come to the place where we are told God directly intervenes, and therefore must address it. God sends "an evil spirit" to deal with Shechem, and causes a lot of trouble for them, and for Abimelech in particular. This is an odd moment, no doubt, and actually one among many in which it seems very clear that God is doing something evil, which should be against God's character, right? It's my understanding that many Jews have a belief which is shocking to Christians, but I think holds some possible merit: that Satan and other "evil" beings are actually servants of God in a strange fashion. God Himself, due to His own holiness, simply can't do certain things Himself. Thus, He has servants such as Satan to carry out certain tasks, such as tempting evil men to their own destruction, as we see here. This explanation of course would seem distasteful to most Christians, and I expect the Christian point of view would be that this is more of a passive activity on God's part; not so much that He actively sent this spirit upon them, but that He simply allowed it in response to their sin. Either way, the message is clear: Abimelech and the men of Shechem have done evil, and they are going to reap a penalty for it.
The SAB has on odd note about "the men of the tower of Shechem", claiming apparently that 1,000 people are way too many to house in a tower. Well, I have two thoughts about that. One, as the SAB suggests jokingly, I suggest in seriousness that this may have been a really big tower, the text gives no size. (Also, names may be deceptive, as the "Tower of London" is not a single tower, but a palace/fortress comprised of a walled area with about 20 literal towers.) Two, the text mentions "the men of the tower of Shechem", not "the men who lived in the tower of Shechem". There probably was some sort of fortress where these 1,000 people lived that was famous for having a tower, not being a tower. I could be wrong because once again, history is not my best subject, but I believe a tower in those days was not just a defense for itself, but for any walled area nearby, and these people may have simply lived in a walled area adjoining the tower.
Abimelech dies in an odd way. A woman tosses a rock on top of him, and knowing he is about to die, he calls out to his armor-bearer to kill him so that people can't say that he was killed by a woman. Yeah, it's sexist and sort of weird, what can you say? Well, other than the fact that this strange dying wish was apparently a failure. (This bears some similarities to the death of Saul.)
The last note here is on the comment that killing his 70 brothers was less of a crime against them than it was a crime against their father. There are numerous cultural reasons for this sort of statement as I understand it. First of all, it's common in the Bible and in that culture to consider a family to be a collective entity representing the father. Second, and closely related to that, it's considered a very good thing to have many children, and now, Gideon's heritage is essentially gone. Thirdly, even with all the bad stuff that Gideon did in his life, if his story had just ended with chapter 8, his would have been one of the best, at least in this book. Now, it's pretty much especially shameful with this bloody footnote. Murder is an odd thing, I've always said, since the "victim" does not suffer once the act is complete. Those who suffer are the friends and family. Now that everyone in this story is dead and buried, Gideon's children are simply forgotten, but Gideon's heritage is a serious blemish on the face of Israel's history.