I'm Spain and the City-State has a delicious Natural Wonder within its territory. To me this is the only case when a hostile take-over could be somewhat justified.
Shedding a single tear toward Mongolia's UA.
Yes...in my current game I did just that....A nearby city state had the only reasonable access to both Great Barrier Reef tiles.... So I captured it, something I rarely do, but it seemed to make sense this time.
[Aside: I noticed something interesting before capturing the city state. I was allied with this particular city state...returning workers...capturing Barbarian camps...the usual. Then all of a sudden I was given 1000 G when the city state grabbed a sea tile and exposed the GBR....I had no units nearby to actually see it for myself, but because I was an ally I got the credit for the discovery....I hadn't realized the game mechanic worked this way. Another reason to consider allying some city states....you may get credit for some natural wonder lurking in the fog nearby.....]
But, wow, it has turned into one of my most interesting games in a long time.
The closest AI is India and, well, it didn't take long before I was denounced...which I expected, and although I was building up my military anyway....to eventually grab wonder-stuffed Delhi..... Gandhi DOW'd before I really expected it. And sent a G&K-type swarm of units towards Madrid.
And something that hasn't happened to me for a while... I lost my capital...

But Gandhi couldn't hold it. I got it back about three turns later. I also managed to capture his second city, Mumbai...and proceeded to raze it, but could only hold it for about five or six turns, then he took it back.
I thought of "rage-quitting"...

But actually this has turned into a rather riveting game..... I have a feeling that I will eventually prevail and capture Delhi and then maybe win a cultural victory, but it's still too early to tell... He DOW'd again, though gave me a reasonable peace settlement ...some GPT... Hey, there is still something disconcerting about being DOW'd by Gandhi, isn't there?
I don't think I've ever been "put on the ropes" quite so badly since starting with BNW and I kind of want to see if I can pull an eventual win out this mess.... Oh yes...I'm playing this out at the Emperor level...
And, yeah, a tear for Mongolia...when I play as the Mongols now, I'm finding that if you are going to be a warmonger...and why else would you be playing as Ghenghis, it seems rather than capturing the city states you want to be able to buy them off as allies to get the luxuries...happiness seems to be in short supply in the Mongol Empire.