Just one part of that is the origin of the D&D alignment system, in its most coherent state of Law-Balance-Chaos. For the purposes of commentary, criticism, teaching, and scholarship (and so the larger internet community can find it) I present the key passages below. Read this, and then the next step would be start reading some classic Michael Moorcock stories about Elric, which expands on the system (with an overview here).
He let the dwarf growl on for a long time without learning much. Hugi wasn't very bright, and a backwoodsman as well. Holger got the idea that a perpetual struggle went on between primeval forces of Law and Chaos. No, not forces exactly. Modes of existence? A terrestrial reflection of the spiritual conflict between heaven and hell? In any case, humans were the chief agents on earth of Law, though most of them were so only unconsciously and some, witches and warlocks and evildoers, had sold out to Chaos. A few nonhuman beings also stood for Law. Ranged against them was almost the whole Middle World, which seemed to include realms like Faeries, Trollheim, and the Giants -- an actual creation of Chaos. Wars among men, such as the long-drawn struggle between the Saracens and the Holy Empire, aided Chaos; under Law all men would live in peace and order and that liberty which only Law could give meaning. But this was so alien to the Middle Worlders that they were forever working to prevent it and to extend their own shadowy dominion.
The whole thing seemed so vague that Holger switched the discussion to practical politics. Hugi wasn't much help there either. Holger gathered that the lands of men, where Law was predominant, lay to the west. They were divided into the Holy Empire of the Christians, the Saracen countries southward, and various lesser kingdoms. Faerie, the part of the Middle World closest to here, lay not far east. This immediate section was a disputed borderland where anything might happen.
He lost sight of the camp as he wandered on, trying to fit what he had learned into a pattern. This business of Chaos versus Law, for example, turned out to be more than religious dogma. It was a practical fact of existence, here. He was reminded of the second law of thermodynamics, the tendency of the physical universe toward disorder and level entropy. Perhaps here, that tendency found a more... animistic... expression. Or, wait a minute, didn't it in his own world too? What had he been fighting when he fought the Nazis but a resurgence of archaic horrors that civilized men had once believed were safely dead?
In this universe the wild folk of the Middle World might be trying to break down a corresponding painfully established order; to restore some primeval state where anything could happen. Decent humanity would, on the other hand, always want to strengthen and extend Law, safety, predictability. Therefore Christianity, Judaism, even Mohammedanism frowned on witchcraft, that was more allied to Chaos than to orderly physical nature. Though to be sure, science had its perversions, while magic had its laws. A definite ritual was needed in either case, whether you built an airplane or a flying carpet. Gerd had mentioned something about the impersonal character of the supernatural. Yes, that was why Roland had tried to break Durendal, in his last hour at Roncesvalles; so the miraculous sword would not fall into paynim hands...
The symmetry was suggestive. In Holger's home world, physical forces were strong and well understood, mental-magical forces weak and unmanageable. In this universe the opposite held true. Both worlds were, in some obscure way, one; the endless struggle between Law and Chaos had reached a simultaneous climax in them. As for the force which made them so parallel, the ultimate oneness itself, he supposed he would have to break down and call it God. But he lacked a theological bent of mind. He'd rather stick to what he had directly observed, and to immediate practical problems. Such as his own reason for being here.
There were still many miles of wilderness to travel on the other side of the range, but she had seen a few clearings, isolated farmsteads, and hamlets. "And where'er several men dwell, if they be not evil doers, will belike lie hallowed ground -- a shrine, if naught else -- which most o' the creatures that dog us dare no approach closely."
"But in that case," Holger asked, "how can the Middle World even think of seizing human land?"
"By help o' beings who need no fear daylicht or priestcraft. Animals like yon dragon; creatures wi' souls, like bad dwarfs. However, such allies be too few, and mostly too stupid, to have more than special use. Chiefly, methinks, the Middle World will depend on humans who'll fight for Chaos. Witches, warlocks, bandits, murderers, 'fore all the heathen savages o' the north and south. These can desecrate the sacred places and slay such men as battle against them. Then the rest o' the humans will flee, and there'll be naught left to prevent the blue gloaming being drawn over hundreds o' leagues more. With every such advance, the realms of Law will grow weaker; not alone in numbers, but in spirit, for the near presence o' Chaos must affect the good folk, turning them skittish, lawless, and inclined to devilments o' their own." Alianora shook her head, troubled. "As evil waxes, the very men who stand for good will in their fear use ever worse means o' fighting; and thereby give evil a free beachhead."