Prologue

The Guardian Gods and Goddesses known as the Twelve watch over the city states of the realm of Eorzea:- the seafaring nation Limsa Lominsa in the La Noscea Region, the desert nation of Ul'Dah in Thanalan and Gridania, ensconced in the Black Shroud. The continent these vast lands and islands are on are known as Aldenard..
These nations carved out a history of blood and betrayal as they each waged long and bloody wars over territory and trade against each other and even sough to impose uncompromising interpretations of their patron God's wills. The fate of Eorzea would soon change though, fifteen years prior a new threat appeared from the East, the mighty Garlean Empire. With its vast armada of Behemoth airships and warriors brandishing weapons that spewd streams of fire it crushed the most powerful of the six known Eorzean states Ala Mhigo out in the deserts of Thanalan.
Galvanised by the fear of a common enemy the remaining city states set out to form a clandestine alliance, however the imperial invasion never materialised and the realm slipped into an uneasy calm.
As the various city states continued to amass their armies a growing number of mercanaries and adventures found themselves without employment and concerned at the rise in the number of these people resorting to less savoury means of survival the city states gathered together to form a network of guils. These guilds provided the adventures and Mercs a chance to utilise their talents for the benefits of themselves and others.... the age of adventure had begun.

(slightly adapted from the FFXIV manual)