To start, magic is fairly new to humanity. Magic has only existed for humanity for about five hundred years, Since the great fall. The great fall is the phenomenon where five hundred years ago humanity nearly drove itself to extinction.
Thanks to continuous war humans had destroyed forty percent of their population. Not soon after did the demons attack what was left of the already dying human race. Because of the human wars, they were not only caught off guard but defenseless as well. Before they knew it they another thirty percent of the human race was wiped out by the demons. They were lead by the Devil King. Despite them being called demons there is more than one race that claims that title.
First is the devils. They resemble humans mostly, the only thing setting them apart being their horns, white hair, red eyes, and bat-like wings. They have immense magical power and physical strength and are especially adept at using fire and forbidden magic. The devils are considered the most dangerous demons of all. They normally only attack at close range. They are ranked based on strength the strongest being the Devil King.
Second is the dark elves. Unlike the moon elves, they sided with the devils during the great fall. They resemble humans as well, being set apart only by their pointed ears, pale skin, and red eyes. Their physical power is similar to that of a normal human but their magical power is stronger than even that of the devils. They mostly use wind magic but in rare cases, they can use fire magic. They attack from a range and use their environment to their advantage. They rank each other based on intelligence.
The other high ranking demons are the Demon Lords, the dark knights, and the dragons. The other demons are low ranking and less powerful. These include werebeast, beastmen, vampires, magical beast, and goblins. While these demons are less powerful they can easily overpower humans.
The demons had soon taken control of most of the world. After over half the human race was wiped out the other races joined together to stop the Devil Kings army. These races included the moon elves whos magical ability could topple entire cities, the dwarves whos earth magic and raw strength helped turn the tide of the war, and the four chosen vessels of the four gods who slew the devil king and drove back his forces with strength beyond any of the other races both physically and magically.
After the Devil Kings' death, most of his army had scattered. The dark elves taking to the forest and creating small villages, the devils going across the sea and creating what is now called wilderia, taking in all demons willing to join them, and the dragons disappearing without so much as a trace to follow.
When the war was over for good it was the moon elves who taught humans how to use magic. Most of the technology of the old day was lost the knowledge dying out after the end of the war. Many people tried to find the old world's knowledge, but those who were seen again had never even gotten so much as a glimpse at what the past held. Many drove themselves to madness trying to find out what we had lost until it was declared illegal to search at all.
Using magic is fairly easy as all one needs to do is find what element is easiest for them to control. Most people find this out by the age of ten sometimes sooner. To use spells humans adapted to using magic books called grimoires to help control their output of mana. Mana is the energy inside all living and nonliving things. To use magic one must control the mana inside themselves and the element in which they want to control. A spell is a combination of multiple elements and magic types to form unique magic. No grimoire is the same for two people, each holds a magic unique to the one to the person it is given too.
Once the elves taught humans to use magic the returned to their forest leaving the humans to find what was left for them in their war-torn world. The humans that were left after the war eventually came together to form a gigantic empire. They learned to use magic in their daily lives to help rebuild their homes and cities but with the threat of the demons still eating at their heels, they were forced to make another army under the four gods' vessels leadership. Soon the demons became less and less of a worry and the army became less and less needed. After a while, the threat dissipated completely and the army disbanded leaving only a few thousand to guard the great kingdom.
The four gods vessels soon began to die living for hundreds of years to protect humanity and all the other races from the demons. But soon age caught up with them and they all died out leaving the message that the demons would rise once more and at that time new vessels will be chosen. The human celebrated their deaths and mourned the loss of their saviors with parades every year.
A hundred years after the death of the four gods vessels an academy was formed to help train young mages to use magic properly and to bestow new grimoires to the next generation. This academy was named the Moon Towers in honor of the moon elves who taught the humans to use magic. The towers are governed by the head administrators who answer only to the king of the empire.
No one has ever heard from the demons since the great fall, bringing the dying words of the vessels into question. Many wonder if the vessel's words were true, and if so why have the demons been so quiet for so long? Why not attack them before they attack us? What's stopping them from finishing off humanity now that the vessels are dead?
It is these questions that motivate humanity to train new mages, to rebuild their old armies. To prepare for a war that may never come.