In the lore of Dungeons & Dragons, demons and devils are two unique orders of fiends, the denizens of the lower planes. From the roiling depths of the Abyss, Demon Lords rally the unruly lesser demons into bloodthirsty hordes. Beneath them, the Archdevil Asmodeus rules legions of devils from his seat of power, the Throne of Baator. Both are the epitome of evil, yet their opposing natures have led the demons and devils to engage in a cycle of incredible violence known as the Blood War.

The sparking incident of the Blood War has been lost to time, but many sages agree that it continues due to the intrinsic nature of both types of fiends. Demons are beings of unmatched cruelty who wish for nothing short of unmaking reality. They despise order in any form and seek to sow as much chaos as possible. Devils are tyrants, seeking to bring order to the multiverse, bending all to the will of Asmodeus. They have a clear, militaristic hierarchy. While they are always looking for opportunities to rise in the ranks, devils follow the commands of their betters. Devils are also forged from the souls of evil beings, lured into their ever-swelling ranks.

RELATED: Dungeons & Dragons Does Greek Mythology In Magic: The Gathering Theros Crossover

Avernus, the first layer of the Nine Hells, is the most prominent battlefield of the war. The Abyss sits above the Nine Hells and the River Styx, which connects all of the lower planes, providing the perfect avenue for the demons to invade. Occasionally, the Devils push upward and fight the demons on their home turf of the Abyss. The battle lines of the war are constantly undulating as territories are repeatedly conquered, lost, then conquered again. This has led the Blood War to sometimes be referred to as “The Great Dance.”

The war manages to escape the bounds of the lower planes and spill out into the material plane. Mortal cultists worshiping Demon Lords and Devil Princes act as agents for their patrons, frequently performing assassinations, procuring powerful artifacts, or enacting dark rituals to curry favor. Any secret uncovered may lead to the winning edge that will allow one side to finally topple the other.

It may seem like a good thing that devils and demons are constantly at war, but when it reaches the realm of mortals, the effects are frequently devastating. Neither side has any concern for collateral damage, and entire villages are often razed to the ground just to ensure that no enemy survives.

RELATED: Dungeons & Dragons: Why Your Next Game Should Enter a Funhouse Dungeon

There’s no lack of reinforcements either. Demons are spawned from the incomprehensible chaos of the Abyss and grow in strength and form the longer they survive. Devils, on the other hand, are formed from the souls of those bound to demonic contract or beings who were so evil in life they are given the offer to join the ever-growing legions. To further complicate matters, a fiend can only truly be killed on its home plane.

A demon killed in Avernus will dissipate and reform back in the Abyss fully restored. Likewise, any devils who die in the Abyss will awaken to find themselves once again amongst the ranks of their fellow soldiers. Since most of the fighting takes place in Nine Hell's first layer, Avernus, it may seem like a bad deal for the devils, but in fact, they prefer it.

Devils are cunning tacticians, and they know if they pushed too hard into the Abyss, it would become too hard to maintain supplies and the proper influx of forces. A devil killed in the Abyss may return, but their powerful weapons and armor will be left behind. Plus, devils are always seeking out souls to corrupt. As long as there is life, the devils can ensure a steady supply of new troops.

RELATED: Dungeons & Dragons' Greatest Wizard Is More Than a Gandalf Rip-Off

Demons, though typically depicted as a mindless beast, are more cunning than they are given credit for. It may seem like insanity to attack the same realm again and again to no avail, especially when there are other realms that exemplify the order they despise. Demons could easily invade the righteous Mount Celestia, home of angels and the gods of goodness. But doing so would play right into the devils’ hands.

The Demon Lords know if they were to invade another realm, even a good one, the devils would join in and assist, allying themselves with the likes of celestials just to ensure victory over the demons. The demons know that this feeling is not reciprocal. There are no forces of good coming to the defense of the devils. By concentrating their attacks on the Nine Hells, they limit the devils’ strength.

Devils take their role in the war with pride, believing that the denizens of all other realms owe them their gratitude. Demons would unmake everything if given the chance, and it is only by their unwavering discipline that the planes continue to exist in peace. Of course, any safety they provide tends to be overlooked because, if given the chance, the devils would descend upon the planes and beat all life into subservience.

RELATED: Dungeons & Dragons: What a Dragon’s Color Actually Means

Fiends from the other lower planes, like the yugoloths of Gehenna, are also hired as mercenaries. They will fight for demons or devils, whoever is the highest bidder. It’s a good deal for the yugoloths, as most of the fighting happens outside their home plane. If they die in Avernus of the Abyss, they’ll simply return to Gehenna. Yugoloths are reluctant to fight on their own plane and risk permanent death, so any contracts to ensure their services in such a battle would be quite costly.

There is a legitimate fear among many sentient beings that, if one side were to prevail over the other, the one which remains may actually stand a chance at achieving their goals. This has led to the development of a philosophy called “The Balance.” Adherents of the Balance believe that the stalemate between demons and devils must continue at all costs. It requires a being capable of understanding the immense scope of the Blood War to fully embrace the Balance.

Followers of the Balance will save a town from demons with one hand and allow devils to claim the souls of vicious warlords with another. Most people find the Balance confounding and a morally compromised ideal. Famed wizard Mordenkainen is a firm enforcer of the Balance, believing fully that the Blood War must continue so the fiends can focus their onslaughts on one another. So far, his efforts have not been in vain, as the millennia-long Blood War is poised to continue for millennia more. Should either side win, it would spell doom for us all.

KEEP READING: Welcome (Back) to Underdark, Dungeons & Dragons' Deadly Subterranean World