So as anyone who has played Final Fantasy XIV: A Realm Reborn can figure out, the realm of Eorzea has undergone quite a few changes since FF14's humble, kinda bad, and confusing beginnings.

Just like in ARR, your intro is determined by which city you decide to start in. Start in Gridania, you meet Papalymo and Yda while running away from rampaging treants during a walk through the Shroud, and you learn of the Elementals and the Greenwrath. Start in Ul'dah, meet Thancred during a parade where a "tame" Goobbue loses control and learn about Minfillia's father, who was an Ala Mhigan spy. Start in Limsa Lominsa, meet Y'shtola on a ship that's attacked the by the Thalaos and some jellyfish enemies, and also get the earliest exposure to the core enemies in A Realm Reborn: the Ascians, and a sneak peak at an innocuous horn that proves to be important much later…

After the conclusions of the city-state story lines, the story converges on the Path of the Twelve; an independent organization of people blessed with the Echo, working together to understand their gift and hopefully use its power for the good of Eorzea. This includes using the Echo's handy-dandy anti-Tempering abilities to stand up to the first Primal formally introduced in the game: Ifrit. Some time after confronting Ifrit, the Path of the Twelve comes into contact with an Ala Mhigan resistance cell intent on stealing an Imperial airship and using it against the Empire. Needless to say, the plan fails. All thanks to one man: Gaius van Baelsar.

Gaius' introduction:



Some time after Gaius' rockin' intro, news spreads of the arrival of another Garlean legatus: Nael van Darnus, head of the VIIth Imperial Legion. Nael's arrival in Eorzea also coincides with the arrival of several characters important to ARR: the heads of the Grand Companies (Admiral Merlwyb Bloefhiswyn, Elder Seedseer Kan-E-Senna, and Flame General Raubahn Aldynn), Cid nan Garlond, Urianger Augurelt, and Louisoix Leveilleur.

All of these players converge on Eorzea during a time known as the Seventh Umbral Era. The Umbral Era was heralded by two unsettling things: the change in monster behavior, and the appearance of the lesser moon Dalamud growing brighter in the sky. The Grand Companies investigate these phenomena, which eventually lead to the revelation that the Empire planned to carry out the "Meteor Project", which was an attempt by the Empire to purge Eorzea of the Primal threat.

While the Empire gathered Allagan Runestones (which were necessary for Dalamud to be drawn to the planet), they carried out a large number of seemingly random skirmishes against the three city-states to distract them while they built Castrum Novum, a military base in Mor Dhona which housed the Lunar Transmitter used to bring down Dalamud. An alliance of the Grand Companies and adventurers were able to attack the Castrum and destroy the Transmitter, but it was too late: Dalamud's descent was not stopped, and Nael (seemingly) had power over the moon's fall.

Cutscene following the attack on the Lunar Transmitter:



After the destruction of the Lunar Transmitter, Nael is found at Camp Glory (in Coerthas Eastern Lowlands, which is inaccessible in ARR). He rains debris down from Dalamud which creates the arena for the battle against Nael - the Rivenroad.


The death of Nael van Darnus and the destruction of Rivenroad proved to be inadequate to stop Dalamud's descent, so Louisoix sent the Warrior of Light on a pilgrimage around Eorzea to pray to stones scattered throughout the realm bearing the insignia of the Twelve on them. Louisoix's final gambit to protect the realm from Dalamud's fall was to call the Twelve in a manner similar to Primals, but…




For more info on the Seventh Umbral Era (even had to use this to close some gaps in my memory) go here: http://finalfantasy.wikia.com/wiki/Seventh_Umbral_Era