"Medieval" by definition refers to the Middle Ages: "The period in European history between antiquity and the Renaissance, often dated from a.d. 476 to 1453." [source] We can squabble over just how wide a swath, geographically, this refers to, but generally speaking this does not include East Asia, South and Central Africa, Australia, or the Americas.
I believe the date range Tom mentioned goes from 700 to 1300. The latter date may be off (1500? I can find it again tomorrow), but I do remember the earlier date specifically. So any justification for things that are reasonable should demonstrate to have been applicable during that specific time period. No justifications of "The Greeks did it this way in 300AD" or "the Romans had this in 300BC" unless
it was still being done by 700 AD. It also means nothing that was invented in 1585, let alone 1985. And even if it occurred in 300 AD and then again in 1800 AD, if it didn't happen during 700-1300, then it's out. So no Roman war chariots.
And also important to keep in mind is that SMA is specifically geared toward European geographic locales. "The Chinese did it" is no more justification for something being valid than "the native Americans did it". A Japanese Shogun realm is no more valid in SMA than is an Alaskan Inuit tribe. The general flavor of things should be European. This doesn't mean "If it has Oriental influence it's forbidden". It means that the primary inspiration and flavor should be European. (I believe Tom's words were something like "A little bit of the Orient spices things up, but if everyone does it, then it ruins the atmosphere.")
This also does
not mean that you have to find the exact situation/organization/concept as an RL analogue for what you want to do. Otherwise we'd pretty much all be playing Christian Crusaders. But the overall feel and atmosphere should be decidedly European medieval.
What you do needs to actually be physically plausible. No anime-style little girls wielding gigantic 300 pound broadswords while riding sparkly talking wolves into battle. (Like someone was trying to RP on FEI not too long ago...)
And, finally, it is also important to remember that SMA is not intended to empower you, or free you to do whatever you want so long as you're serious about doing it. It intentionally limits what you can do. True, these limits are broad, but they are still there. And it is up to us as players of this game to make sure that what we do fits in there. And also to call out anything that we feel does not fall within this framework that we've been given.
I don't know if any of that makes anything simpler, or more difficult.
