—From the opening lines of each novel
The Fourth Age of the Wheel of Time is the age prophesied to follow the Third Age and the Last Battle against the Dark One. It is an age that lies in the near future from the perspective of the people of the world; alternately it is a very distant age long past.
Several excerpts of the histories of the Fourth Age exist. According to these fragments, cities such as Great Aravalon, a possible incarnation of Tar Valon, and Taralan will exist in the Fourth Age. A place known as the Court of the Sun will also exist.
In 1000 NE, Aviendha experiences a vision of the future from the glass columns in Rhuidean, providing a glimpse of what is presumably the Fourth Age through the eyes of her daughter Padra and subsequent descendants.
Approximately 17 years after the Last Battle, the Aiel find themselves restless, having been excluded from the Dragon's Peace and lacking a unifying purpose with the Last Battle concluded. They decide to go to war with the Seanchan when negotiations to reclaim their captured Wise Ones break down with the new Seanchan empress, Fortuona's successor. Some 40 years after the war began, the Aiel and Seanchan were locked in stalemate, with Rhuidean besieged. Padra's daughter Oncala decided to pressure the nations of the Westlands into breaking the Dragon's Peace and joining the war on the Aiel's side by deceiving Queen Talana of Andor, knowing that Talana's influence would draw in the nations under the Pact of the Griffin and the Court of the Sun. Oncala presented Talana with Seanchan invasion plans stolen from the Tarasin Palace; Oncala deliberately withheld the fact that these plans were only contingencies to be used if the Westland nations attacked the Seanchan first.
Oncala's ruse succeeds. Decades later, the war has gone badly for the Westlands and Aiel. Every nation and the White Tower has fallen to the Seanchan, who have gained dragon technology from the conquest of Andor; the Asha'man continue to fight, but no longer hold the Black Tower. The remaining Aiel, greatly reduced by the constant warfare, decide to retreat to the Aiel Waste to rebuild their strength, but to no avail. The Seanchan, now known as the Raven Empire, develop firearms and other new technologies that the Aiel cannot counter. They hound the Aiel throughout the Waste, attacking any gathering of three or more Aiel and even persuading the Far Ones to avoid aiding the Aiel in any way. The Aiel attempt to make one last, secret hold, but this too is razed. The last Aiel scatter and become impoverished nomads unable to support themselves, eventually degenerating into a near-feral scavenging people who call themselves the Folk.
By then, the Raven Empire seemingly dominates the Westlands uncontested. The Empire's technology has advanced to the point that firearms, automobiles, and electric lights are commonplace, and a railway is being built across the Aiel Waste to link the Empire with Shara.
It is ambiguous as to whether this vision shows what will occur or what could potentially occur. Since Aviendha forces Rand to include the Aiel in the Dragon's Peace as a result of her vision of the Aiel's fall, however, it is possible that this particular future was circumvented.
Throughout the novels in the Wheel of Time series, there are scattered excerpts from historical documents which are dated from the Fourth Age. This seems to suggest that the books are being written, perhaps by Loial, after the Last Battle has occurred.