Help me remember which book this was:
Highly advanced aliens show up at Earth and try to save us from ourselves. Like confiscating a kid’s army-men set until he gives up hitting his brother, the aliens make Jerusalem disappear until we stop making war on each other. The entire city disappears, and where it used to be is some kind of weird melted place. The aliens promise we can have it back once we learn our lesson.
???
TIA!
I think you are looking for The Fresco, by Sherri S Tepper.
At least, Jerusalem disappears in that one, I don’t remember anything about toy army men.
pipperroo is correct, it’s The Fresco. “Toy army men” is just the OP’s metaphor.
Yes! That’s it exactly; thank you! And sorry about the confusing analogy with the army men.
Heh. That sounds like my longstanding notion of giving Jerusalem to the Japanese to turn into a theme park.
Still haven’t quite figured out who to give Northern Ireland to…
Tepper is one of my favorite authors.
I just wish I could find a reasonably priced copy of her Mauven Manyshaped trilogy.
*The True Game *(omnibus edition of the Mavin Manyshaped trilogy) for $4.49 
Rats – sorry, it looks like there’s more than one omnibus from the True Game collection and the The True Game I linked isn’t the Mavin set but rather King’s Blood Four, Necromancer Nine, and Wizard’s Eleven. And of course as you probably already know, the Mavin omnibus set is The Chronicles of Mavin Manyshaped and isn’t available. 
My personal solution was to take Jerusalem and transport it (either piece-by-piece, or by magitech) to…the Bikini Atoll.
I was just going to have the Imperial Corps of Engineers sink Northern Ireland, if it got out of hand again.
I’ve just finished Fresco, and read Grass not too long ago. Like both of them, even if they were not quite as challenging as some of my favourite SF (maybe it’s because I basically agree with her?), but now I have one question:
Do all her SF books have human-on-alien nookie as an ideal relationship, or is it just coincidence with the two I’ve read?
Hmmn. Quite a few do, though more have oppressive, male-dominated religions or social hierarchies based on spurious foundations. I think the alien-as-love-interest thing is more a function of that – like, as in, “Look, even an *alien *is more desirable than the local male chauvinist humans.”