The campaign was set in the Eberron setting by Keith Baker. The setting is centred on the continent of Khorvaire, which has just emerged from the hundred year Last War that rocked Khorvaire, ended the Kingdom of Galifar, and destroyed the entire nation of Cyre in the magical cataclysm known as the Mourning four years ago. The Last War ended two years ago with the signing of the Treaty of Thronehold that officially split Galifar into twelve new nations.
A complicated web of politics and intrigue is played out by the Five Nations, the newly established nations, and the powerful Dargonmarked Houses, merchant dynasties that have grown fat on the commerce generated by the war. The Dragonmarked Houses grew around the Dragonmarks, magical marks that started appearing within some families several thousand years ago. These Dragonmarks are related to the Draconic Prophecy which charts out the future of Eberron and can be read in complex relations between different signs and portents, Prophecy Marks scattered across the landscape and the people. The Draconic Prophecy is fluid and complex to interpret, and hints both at events of doom and destruction as well as exalted events, but seems to point more to transformation than destruction.
A lot of the economy of Eberron centres around the Dragonshards, magical crystals that are produced by the three parts of the world and are a necessary component in things like the Lightning Rail, Elemental Airships, and many other magic items.