The Borderlands are the Westland nations which lie furthest to the north and directly border the Great Blight. Ten nations have been part of the Borderlands since the Breaking of the World, although the term did not come into use until at least the time of Artur Hawkwing, if not much later.
During the War of the Hundred Years the five Borderland provinces of Saldaea, Kandor, Arafel, Shienar, and Malkier broke away from Artur Hawkwing and declared both independence and also an alliance with one another, agreeing to aid one another against both the Shadow in the north and any attempts by the southern nations to attack them.
Malkier was destroyed by internal betrayal and external attack in 955 NE. Its territories were consumed by the Blight. The four remaining nations share a military lifestyle of constant vigilance against the Blight to the north.
For 3,000 years the nations of the Borderlands have guarded the Westlands against Shadowspawn from the Blight. The culture of the Borderlands is the most martial of all Westlands and many of the best soldiers hail from the Borderlands. Because of the Borderlands' close proximity to the Great Blight and Shayol Ghul, Aes Sedai are highly respected and revered.
In the Borderlands, all men carry swords at all times in case of attack. Due to the constant threat, no country in the Borderlands has a distinct elite military formation.
The Borderlands do not concern themselves with the affairs of southlanders. However, in 998 NE Moiraine Damodred and al'Lan Mandragoran, the heir to Malkier's throne, came to Fal Dara in Shienar with a party of Andorans and an Ogier. In a quest that rapidly became a legend in the Borderlands, they found the legendary Eye of the World and the Green Man, and are credited with somehow turning the tide of battle at Tarwin's Gap, where the army of Shienar was about to be overrun by a Trolloc horde ten times larger. After this, a party of Shienarans, including a sniffer named Hurin, accompanied these travelers on a series of adventures culminating in an epic battle at Falme where Rand al'Thor was proclaimed the Dragon Reborn.
This information is collected from the Wheel of Time Wiki located at http://http://wot.wikia.com/wiki/Tower_of_Ghenjei.
And for those wondering about the connection to the books and this locations name, this is the county border between Sacramento & El Dorado.