"Now, Demacia is a kingdom in turmoil." That is Riot's own overview, one paragraph in, after the justice, the honour and the duty. The kingdom that was founded to keep magic out has discovered that magic was inside it all along, in its crown prince's closest friend, in the sister of its greatest soldier, and in a colossus it built to protect itself.
This is the hub for Demacia: what it is, what petricite does, why it is breaking, who lives there, and what it would be in the Riot MMO. The game parts are speculation and say so. The rest is Riot's.
What Demacia is
A kingdom in the west of Valoran, self-sufficient, martial, and, in Riot's word, "insular". Its founders were refugees from the Rune Wars, the thousand-year-old catastrophe in which the World Runes were used as weapons, and they built their capital, the Great City, as a refuge from sorcery. The Great City is the region's landmark on Riot's interactive map, provided as a three-dimensional model, and it is built from the substance that made the refuge possible.
The founder was Orlon, a man the myths remember as a giant-slayer, and the hammer he carried is the one Poppy has been trying to give to a worthy hero ever since. The kingdom he founded took his caution about magic and, over the centuries, made it a law.
Petricite is a white stone that dampens magic. Demacia's walls are made of it, its armour is lined with it, and its laws are written around it: magic is not merely distrusted in Demacia but policed. The Mageseekers are the order that does the policing, and the persecution of mages is the region's defining injustice and, in the current lore, the cause of its crisis.
Why it is in turmoil
Sylas, a mage the Mageseekers imprisoned, broke free, raised a rebellion of the persecuted, and killed King Jarvan III. His son Jarvan IV took the throne of a kingdom that had just learned its enemy was its own policy. Lux, the sister of Garen, the kingdom's most famous soldier, is a mage hiding in plain sight at court. Galio, the petricite colossus built to defend the city, is animated by the very magic he was built to absorb, which is the region's contradiction cast in stone. Kayle and Morgana, the winged sisters of Demacia's founding myth, have returned, one to judge and one to forgive.
Riot has spent several years turning a region that used to be the setting's plain heroes into its most conflicted, and the Marvel comic Lux and the Riot Forge game The Mageseeker were both written to tell that turn. It is not resolved.
Who lives there
Riot's roster, sixteen strong: Fiora, Galio, Garen, Jarvan IV, Kayle, Locke, Lucian, Lux, Morgana, Poppy, Quinn, Shyvana, Sona, Sylas, Vayne and Xin Zhao.
The crown: Jarvan IV, and Xin Zhao, his bodyguard. The army: Garen, who commands the Dauntless Vanguard; Quinn, the ranger whose story "Shield of Remembrance" is one of the five we recommend in where to start with Runeterra; Shyvana, a half-dragon the kingdom tolerates because she fights for it. The nobility: Fiora, the finest duellist in a culture that settles things by duel. The hidden mages: Lux, and Sona, whose music is magic and whose silence has kept her safe. The rebel: Sylas. The hunters: Lucian, who hunts the undead with the guns his wife left him, and Vayne, who hunts the magical for reasons of her own. The founders: Kayle and Morgana, and Poppy, a Yordle carrying a hammer meant for a hero she is still looking for. The colossus: Galio. The newest name is Locke, whose title, the Ashen Exorcist, tells you which side of the kingdom's argument he is on.
The places
The Great City, and within it the Petricite Hall and the Grand Plaza painted for Legends of Runeterra. The Mageseeker compound. The border forests of the Eastweald, where Quinn's story is set. Legends of Runeterra gave Demacia 185 cards, the fewest of the six major human nations, which says something about how much of the kingdom is still undrawn.
Demacia in the MMO, as a guess
A reading, not a report. Riot has confirmed nothing about which regions ship, or how.
Demacia is the setting's most legible region: a kingdom, an army, a law and a secret, in one sentence. That is what a starting zone needs, and it is why Demacia appears first in nearly every fan account of the game's opening and in ours, in starting zones. It connects by land to the Freljord and to Noxus, its opposite in every value, and the border between the two is the setting's oldest war, which is the case we make for it in Riot MMO PvP.
Inside the kingdom, the persecution of mages is a quest engine that needs no invention: a Mageseeker faction to join or resist, a court with a secret in it, a rebellion in the countryside. And petricite is a mechanic waiting to be built, a material that suppresses magic in a game where magic is half the class list, which we work through in Riot MMO classes. A Demacian mage-hunter is a class no other setting can offer.
The turmoil is a problem for the game as well as a gift. Whether Jarvan IV is a new king or a settled one depends on the era Riot chooses, the open question in when is the Riot MMO set?
What we do not know
Whether Demacia is a starting region, and whether region and race are the same choice, as discussed in playable races.
Whether the game takes a side in the mage question, or leaves it to the player.
Whether the Kayle and Morgana myth is background or plot.
For Demacia among the other twelve regions, with the numbers, see the 13 regions of Runeterra.