The demons, also known as "Baldricks" are the primarily antagonists of Stuart Slade's science fiction web-novel, the Salvation War: Armageddon.
The novel is a combination military science fiction and deconstruction of the apocalyptic horror genre, in which God announces that heaven is closed to all humans and orders all of humanity to die. While religious fundamentalists respond obediently to the message, believing themselves to be the exception to the statement that all of humanity is damned, most of humanity goes on as normal, until a number of "demons heralds" appear at major cities, declaring Earth under the dominion of Satan. One of these heralds is engaged by a squadron of US Navy F/A-18 Hornet fighter, who discover that the demons are easily killed by missiles and cannon fire. Shortly afterwards, more demons are killed by military and/or police forces in Japan, Russia, Thailand, Singapore, and other countries. The fact that the demons are mortal prompts almost every government on Earth to literally declare war on both heaven and hell.
A portal to hell appears in Iraq, and a demonic army under the demon lord Abigor marches through, including infantry armed with tridents and bio-electricity, as well as flying "harpies" and cavalry riding arthropod-like mounts. These, however, prove no match for human tanks, and are crushed by US, British, Iranian, and other air and armored forces. The demons make a momentarily breakthrough against US infantry at the town of Hit, who discover the demons are practically invulnerable to standard rifle ammunition. However, the US troops regroup, fighting with grenades, AT4 rockets, and .50 caliber firearms, aided by Iraqi insurgents, who kill off numerous demons with car bombs and RPGs.
The international coalition quickly defeats the demonic army, and Satan, infuriated by the demon lord Abigor's failure, sends Abigor and his family to march personally towards the US lines. Seeing no other options, Abigor surrenders and defects to the coalition forces. Meanwhile, a helicopter pilot killed by "harpies" in the intial invasion, a Lt. Jade Kim, and the rest of her squadron, escape for the torture of hell and start a resistance movement, supplied using portals generated by psychics on Earth.
Shortly afterward, human forces invade hell itself, and quickly crush the demonic opposition and set up a base in what they rename the Phelan Plain, after a mall security guard who fought and died against a demon who attacked from a portal, allowing numerous civilians to escape. Demonic counterattacks are decimated by human firepower, including armor, air power, and even chemical weapons such as mustard gas and white phosphorous.
At the same time, it is quickly discovered that the demons are not supernatural beings at all, but extradimensional aliens with extraordinary biological abilities, such as superhuman strength, bio-electricity, mind control pheromones (in the case of succubi) and creation portals using quantum entanglement. Demonic defectors reveal to human intelligence that when humans die, their life force creates enough energy to create a portal into a new dimension, however, when demons (and angels or humans in the new dimension) die, they simply cease to exist, as they do not have the energy to "cross over". Both God and Satan are particularly powerful extradimensional beings who intend to overcome this and enter new dimension by gathering energy, either from human suffering in the case of Satan, or blind faith in the case of God.
In spite of their defeat, the demon Lord Belail manages to find a way to strike at humanity, using the portal-generating powers of nagas to place a portal over over volcanoes. Belail targets two major cities identified as major centers of industry by damned souls: Sheffield, England, and Detroit, Michigan. While thousands are killed, the demons quickly discover their information on industrial centers is outdated- there still exist more than enough factories to produce the tanks and war machines necessary to fight the demons.
In retaliation, the US Air Force drops four massive bunker buster bombs on Satan's fortress in the city of Dis in Hell itself, though Satan himself survives as he was not in the fortress at the time. Meanwhile, Abigor quickly becomes leader of a demonic resistance in opposition to Satan, and spends much time studying human weapons. He is shocked to learn of nuclear weapons and realize that humanity is in fact, holding back its deadliest weapons.
The demonic resistance quickly falls apart as human insurgents assassinate a duke of hell, and another is killed by cannon and missile fire from A-10 attack aircraft. Isreali helicopters attack the arrival point and liberate dead humans arriving in hell, as the "Hell Pit", Dante's nine circles of hell, is liberated, freeing billions of "second lifers" as Satan himself is killed when human psychics create a portal to his inner chambers, where two anti-ship missiles are fired, one striking him directly in the head, killing him. After Satan's death, most of the demons surrender, and are placed under an interim goverment under Abigor, save for one part of hell, which becomes the "New Roman Republic" under Julius Caesar, who joined Lt. Jade Kim in her resistance, and proves to be every bit as skilled a leader in the afterlife.
The human coalition is then tasked with rehabiliting "second lifers" who spent centuries in torture before being liberated, and even setting up a division of loyal demons to aid them in their next war: on heaven itself.