Here's a YouTube video of ChinaSim and the new toy that can actually be seen in video. (As you'll see, ChinaSim is basically impossible to see in video.)
Anyway, one thing the sharp-eyed among you will notice is that the new toy has some distinct weaknesses, one of which is that the trade routes don't tend to run along rivers/coasts. That's not ideal, but I'm just showing the basics, so I didn't bother to refine it. Ideally, the contours of the land play a huge role in what cities can reach which cities: cities on the same river can trade with each other, and cities on a coast can reach a wide range of cities also on the coast. Mountains are hard to cross, and so on. The new sim has some aspects of that, but they weren't turned up enough since I didn't spend any time polishing it.
Another thing that you may have missed is that the ChinaSim cities modify the landscape, while the new toy cities don't. There are two reasons for this.
ChinaSim cities build a lot of stuff. They build farms and mines and such. When I originally built it, the idea was to be almost identical to something like Civilization: a resource-based building game. However, that stuff seems very minor in comparison to trade routes, so I left it out.
ChinaSim cities also chop down forests to bolster their economy. This is fairly realistic: even relatively early societies happily chopped down every tree they could find. It also serves as a handy limiter: when you're out of trees, you're out of an economic free ride. When your population outgrows the wilderness, you have to survive on your trade routes.
It's invisible, but ChinaSim also has a fertility rating for the land, which drains over time. This was implemented specifically to get large, flourishing civilizations to collapse, Fertile Crescent Style.
Those things can be added to the new toy, but even without them, sufficiently large nations tend to tear themselves apart into many smaller, independent nations. So there's no need to engineer a mass famine: the world will never consolidate (or never for long).
There are tons of things I could do with the new sim if I wanted to spend more time on it. One is to replace the per-pixel border claims with regional border claims. I want to split the map into regional blocks of maybe 8-30 pixels in area, split along natural boundaries such as slopes, rivers, and so on. With per-pixel claiming, the nations spend a lot of processor power just thinking about what to claim to what extent (hence the halfassed blotchy look you see in the video). With a regional claiming style, that could be eased and made more realistic.
While I've focused on computer algorithms that automatically generate a world, there are plenty of worlds that are not generated in that way. But hand-drawn worlds have many of the same features, and a game where the player is involved in building the world also has the same features.
Anyway, if you want any implementation details, comment here and I'll provide them.