I'm curious why the time around the Mongol invasions appeals to you more as a campaign setting. Were you wanting to avoid the firearms of the later years, or is there something going on in 1274-1281 that is just too good to pass up?This question is in response to the chart I posted last week listing possible pseudo-historical campaigns to run. I've settled on 13th century Japan, particular the southernmost of the 4 big islands, as the site of my next campaign for a couple of reasons. I've picked Japan off of that list because I'm hoping to lure my nephew into a game or two and at any given time he's obsessed with Naruto, Pokemon, Yu-Gi-Oh, Bleach, etc.
The Mongol invasions of 1274 and 1281 make interesting bookends to a campaign, especially if you center the action on Kyushu, where the Mongols actually landed. Any political equilibrium on the island is disrupted by the first invasion. This attack on the status quo creates a space for PC action (and by action, I mean "bad behavior"). The second invasion was seen as inevitable. You don't send the troops of the grandson of Genghis Khan packing and expect that to be the end of the affair. That means official attention was directed more towards preparing the coast against a new Mongol landing and less in the direction of protecting tombs and ruins from PC predation.
The firearm thing Quibish raises is another issue. Gunpowder is rare and mainly takes the form of Dodongo-disliking Batman-can't-get-rid-of anarchist-flinging bombs. Most days I'm just not keen on arquebuses in my D&D. Ray guns, yes. Historical firearms, not so much. That's just the way I feel about these things. Though there is this one great scene in a Zatoichi film (I forget which one) where some peasants want to rescue their friend from the cops. They're peering over a ridge and one of them says the equivalent of "Holy crap! They've got two guns!" That amused me.
Also there's a bit of an advantage to picking a more obscure period. You aren't going to find a ton of players with fixed opinions about the Anarchy, the way you might by running a game set in the War of the Roses. Running a game set in the same period as James Clavell's Shogun creates a set of expectations. I'd rather spend the campaign filling in a relatively blank slate than fighting preconceptions.
Finally, I'm enchanted with the idea of ending a campaign with the PCs giving Kubla Khan the finger or dying in the attempt.