The UA world of Eberron by Keith Baker and Wizards of the Coast (with some creative liberties and tweaks), where magic, mystery, and intrigue flood the streets of daily life. After spending 100 years warring with each other for control, the war comes to a catastrophic halt with the complete obliteration of one of the warring nations. In its wake, the nations splintered as monsters, war machines, and refugees all struggle to claim power and independence and the original nations try to regain control. Without the war, the dragonmarked houses turn to... other means to make a profit and unknown players step out of the shadows to make their move.
The world of Eberron is mostly unknown to those living in Khorvaire. And the rest of the world? They live in alone, scattered and in fear from roaming monsters and untamed wilds, from demon princes and unknown gods. While Khorvaire offers a touch of each of these across its continent, it was once a strong country made of five nations united (or so they liked to say). These nations were Aundair, renowned for its beautiful cities, and high class living, at least, that was what they liked you to see, Breland, the place of industry, progress, and 'safety deposits' for the local mafia, Cyre, a diversely rich city full of culture, wealth, royal blood, and righteousness, which was completely obliterated in the Mourning, Karrnath, a place of strong military might and pride, with a touch of necromantic magic, and Thrane, known for its strong religion to The Silver Flame, which rules over the land. They were united under the Kingdom of Galifar, a righteous monarchy based in Cyre. When their latest king, King Jarot, died mysteriously in 894 YK with no heirs to the throne, the ensuing power struggle between the Five Nations led to all out war.
Known as The Last War, this power struggle lasted for just over a century (102 years), and what little contact it had with Aerenal became next to nothing. As the war progressed, Dragonmarked houses gained power by selling spies, assassins, mercenaries, and all hosts of new technologies and magics to whichever nation paid them the most, if not to all five at once. As the war progressed, unknown armies began to splinter off and break away from their original nations. However, the war came to a crashing halt when Cyre was obliterated in the Mourning. No one inside the capital survived, and few others across the nation did either. No one knows for sure how it happened. Some say that the overuse of war magic built up into a final explosion of destructive magic. Others say that it was caused by experimentation gone wrong by House Cannith, and still others say that the release of a Demon Overlord destroyed the nation. In any case, the rest of Khorvaire stopped their fighting. By the end of the war, 11 new countries had emerged, and only one had fallen. Although most of the nations are recognized by the original 4 nations, The Demon Wastes and the Shadow Marches refused to follow the laws set out by the Treaty of Thronehold, and Droaam, a nation off monsters, criminals, and others who hope to avoid prying eyes, has yet to be recognized as a nation. While these nations hold stable for now, if the truth of the Mourning comes to light, and war can be continued safely, there is no doubt in any mind that it will pick right back up where it started.
Today, the year is 998 YK, four years after the Mourning, and two years after the Treaty of Thronehold. For the most part, life has gone back to normal. Airships and lightning rails connect most of the major cities across the continent, while magical flames continue to fill the streets of almost every town with light. The nations have resorted to less open means of subterfuge, and warfare is such a dangerous possibility that no one wants to resume it. The remaining warforged have left the armies. Some struck out for a normal life, while others offered their services to a Dragonmarked House. Refugees still flood in from the Mournland, The Shadow Marches, and The Demon Wastes regularly, leaving many western cities overpopulated with the poor. Monsters and outlaws gather together in Droaam, where the rest of Khorvaire cannot reach them. Settlers and archaeologists explore Q'Barra for treasure and hidden wonders. Cultists and demons plot to bring back their overlords and struggle for survival in The Demon Wastes. Meanwhile, gnomes live peacefully in Zilargo, paying no mind as investigators and inquisitives go missing in the night when the try to look into the city's past. Adventure awaits on Khorvaire, and who knows what secrets might be uncovered and which plots must be stopped to prevent the nation from falling into war once again.