A fantasy worldbuilding idea:
Introduction/Concept:
A Post-Tolkien Fantasy, in a sense of exploring the world in an era equivalent of the Fourth Age of Arda, after the great battle against the ancient enemy and the passing of the gods. Exploring the changing world, the emergent new technology like firearms, and new thoughts and religions. And of course, dealing with the legacy of the Gods and the Shadow.
Brief History:
It is the dawn of the fifth century of the Third Age, after the last great war. Although victorious, the world is scarred and people are cast adrift in the new world. It will take great courage and foresight to try to take control and make their own destiny, and many will still fail as this technological and cultural change will be extremely difficult and full of hardships. Some will fall back to the seductive familiarity of the Shadow, others will retreat from the world, trying to resist the change or perhaps to quietly die away from others' eyes.
It should be noted that, while the ancient enemy, who was the primary architect of the Shadow, is gone, it doesn't mean that the Shadow is completely defeated as well. It is now a part of the workings of the universe, as much as the night is to the day, and it has a life and a will of its own. It will rise and rise again, starting an awful fight - an era of horror, death, and change through chaos, before driven out again and taking up new forms. In the forms of cults, Orcs, and those willing to answer the Shadow's call for whatever reason, it will live on, as a shadow of the world under the light, befitting its name.
But it is no longer being controlled and directed by a malevolent will as a tool for their ultimate victory, and that's what makes the Third Age different.
Civilizations:
I don't really have deep knowledge of Islamic Feudalism, but from what I can understand, it is more of a tax-farming and payment system rather than the 'true' feudalism. Of course, in time of weak central government or disunity, it became a de facto feudal system, but even then it was more of a local warlord and strongman defying the centralized authority and asserting his own rule, so technically an aberration rather than the norm.
This being modeled after Middle East-Central Asia, nomadic tribes are a must.
While the regions are not known for democracy or republicanism, it is an intriguing possibility. And well, one of the themes is a change, and it would be interesting to explore the idea of republicanism and democracy in the world of divine royal blood and right.
ME-CA is known for religion, and while certainly carry the risk of racist stereotype, theocracy is also an interesting possibility. Perhaps a great kingdom ruled over by powerful and well-learned monks and monastic orders, or a secret cult manipulating the rulers behind the scene. Perhaps even a Mystical Democracy, combining Sufi-like ascetic mysticism and an idea of democracy.
Races:
Elves are world spirits/Softwares sleeved into human bodies, having a form of the hive mind. They live no longer than humans, but their collective memory and hive mind allow them to clearly remember the past, giving humans the impression of long-lived people, although this also gave them a species-wide permanent PTSD since they literally can't forget. They are known for creating a living technology via plant manipulation, which they use to modify their own body. They have been most badly affected by the departure of gods, having cast adrift without purpose.
Elves can fall under the influence of the Shadow, but their hive mind means the others can quickly realize what is happening and fix the problem. Thus, no Elves ever fought willingly for the Shadow.
Dwarves have rejected both the gods and the Shadow, and are responsible for many religious and philosophical ideas, although often it was the humans who carried and further developed them. Have a strong, collective longing for the past and desire to reclaim lost glories. Having long-studied the works of the world (which is described by them as a great clockwork), and possessing an intuitive understanding and ability to 'communicate' with the stones, metals, and gems, they can unlock the potential and manipulate the environment for their likings. They are also famed for their ability to create semi-intelligent mechanical servants, which accompanies them all the time and perform all sorts of tasks, although they are not interested in creating true sophonts.
Some Dwarves have been seduced by the Shadow. They are probably the most dangerous Shadow cultist, and often take up the leading position.
Humans can be mundane at first glance, except that they are hardier than the Elves or the Dwarves, while simultaneously regarded as sensual by them. Perhaps this is true, but being mundane is an advantage, as they are free of negative side effects of other races' gifts, and have adapted much better to the world after the gods left. Is gifted in prophecy and responsible for the development of astronomy (here, the distinctions between astronomy and astrology are purely arbitrary), as well as known for being great record-keepers.
Also, according to Elves and Dwarves, Humans are attractive, and this is why Elves use human-like bodies. Honestly, I am not sure what to do with them.
Orc is more of spiritual malaise than a race, a form of mass insanity and toxic ideology that drives one to cruelty, depravity, fanatical ignorance, pointless destructiveness, and wicked creativeness, a fantasy Fascism. Some amoral and insane are trying to manipulate this, to create a 'master race' or 'super soldiers', and they themselves are infected by this.
Technology:
Roughly comparable to the 14-15th century Islamic world, but some advanced knowledge, up to the 19th-century level, especially the fields that OTL Islamic world was famous for - clockwork*, physics*, mathematics*, astronomy**, (al) chemistry, and medicine, are known and can be applied via magics.
*Seen as a way to explore and replicate the workings of the world.
**People looked up to heaven to see where the gods went, and if they are coming back.
Gunpowder is a signature technology of the Third Age, and while firearm technology is still at the bombard-handgonne level, they are popular in battle and siege.
Religion:
The gods have all left the world. Perhaps some of them are still here, but if so they are hiding very well. They also locked up many of their secrets and domains, until 'we are ready'. Approaching these is suicidal, as they are very well-defended.
Religion has to adapt. Mysticism focusing on personal salvation and enlightenment is popular, while some people have turned to worship the One God beyond the lesser gods. Most polities are secular (in the sense of something like Confucianism, not modern secular), but most people still do seek out personal spirituality. The Shadow Cult thrives in this environment.
The bad news is that, even as a Korean, I don't know much about the central theme and beliefs of traditional Korean religion, except for bits and pieces. To be fair to me, it is neither the most well-studied subject, nor as well codified as Greco-Roman mythology. Additionally, a lot of them have been mixed up with Buddhism and other religions. Being almost entirely composed of oral tradition, with attempts at writing them down started only recently, it also permanently lost many stories during our turbulent history.
The good news is that I am somewhat more knowledgeable on Islamic beliefs, albeit focused on Arabic than Iranian or Turkic.