(I've played a bit beyond 1 AD, but here's the reaction I had at that point when I read the following.)
Nappy and Democrats were fighting. I even gave the Dems copper to help them out. Then something happened that has
never happened before 
. I didn't know it was possible.
Napoleon back-stabbed me while he was still at war

.
I'm sorry this happened to you, but I'm curious why you called this a backstab? It's not like you had an alliance; you said right here that your trading was helping Napoleon's opponent. I'm not a Deity player, but from some of the games Lain has posted on YouTube, it seems that the AI almost always have the power to crush you, and a big part of playing Deity is knowing the all fine details of the diplomacy mechanics and knowing
exactly how much is necessary to keep a particular AI from taking action against you. So, this time, Napoleon decided he had the power to fight two opponents at once, and he did so...
just as any of us might do in the same circumstances!
As for my own game report, I'm playing the Contender/Emperor save. I settled on the hill 1S. I decided I really wanted to try for the Great Wall, so my early tech was Mining > BW (revolting immediately to slavery) > Masonry. I built a workboat and a worker, whipped a dog soldier and (when that overflow into GW wasn't good enough) a barracks, and completed the Great Wall in 1960 BC. By that point, my warrior had died, defending on a hill against the first barb warrior that had come by. My dog soldier had just killed another warrior who was threatening my mine, and a barb archer moved in to threaten my wounded dog solider. So...it was a close thing, but a successful gamble!
The GW gave me a Great Spy in 1000 BC, which I've sent exploring Napoleon's territory and the land to the west.
At 1 AD, I have five cities. Washington and Lincoln are both plotting, and Napoleon is their worst enemy. He'll also need to be my target, when I'm ready for a war, so the strategic situation looks good!