Cool, I'd be up for this. I've long since wanted to make a collaborative story.

Pirates of the Carribean is 2derivative4me though, so I'd want to mess with that quite a bit. 1700s anglican, Victorian expansion. Perhaps we could play with the Colombus Legend, or Ancient Rome (dem delicious parallels). We could face similar dilemma to Hernan Cortes! And cant forget the zulu and such tribes.

Old seafaring myths could play in too. 

But that's just if you're definitely wanting to write a historical fantasy. I'd personally prefer building a fantasy world, but it's your call!