You can only nuke cities that have no friendly or neutral units in them or near them. If there is even one unit from a player you are not at war with you cannot nuke it...
Hmm, that sounds kind of like it could be something that might be exploited, especially in multiplayer... civs putting units in each others' cities so that they couldn't be nuked, unless the nuker took on
both of their civs in a war at once.
2. Are there any particular tricks for breeding Great Engineers? It's hard when you can assign only one Engineer specialist (from forge) for most of the game, and not many of the early or mid wonders encourage GEs. In my last few games, I haven't gotten any GEs. All I can think of is to try and build all the GE wonders in one city along with your one Engineer and National Epic, and then have a separate co-GP farm with the other wonders and other specialists, but that would be kind of a ridiculous expenditure of effort, specializing your empire around something that is not a victory condition. Probably easier to just stop caring about wonders, but they're important to my vanity.
I think that's kind of the point... it was intentionally done because it's not
supposed to be easy to generate Great Engineers. If it was, then there would be no point in anyone working away at wonder building at all... every single wonder would be built by a Great Engineer very soon after the tech was discovered. And that's just no fun at all.
But as for how you can improve the odds... yes, the early wonders help. The Great Wall is a great cheap source for Engineers. The Pyramids is a good one too of course, though it's expensive and comes during your expansion phase, which is often not great. That's why I'm personally more of a fan of the Hanging Gardens, a very nice wonder that's not too expensive and comes at a good time. Hagia Sophia is alright if you're seriously going for a Great Engineer city (although its natural benefit kind of sucks).
My advice though is don't try to deliberately generate
just Great Engineers, since it's too difficult to do... and even if you do it, you'll be generating them very slowly (since you won't have many GPP's in your GE city). Personally I usually go for a mix of scientists and engineers, as best as a 50/50 distribution that I can get. That way I'm still generating a lot of GPP's, and will still get a Great Engineer on average every second GP, but I also won't be stagnating my GPP's and will be getting a useful GP (Great Scientist) even if I don't get the Great Engineer.
