The Time of Awakening was a period in Vulcan history when the violent and warlike Vulcan race switched to more peaceful ways. It occurred sometime during the 4th century of the Earth calendar, although some Vulcans had already begun to mentally train themselves to suppress their emotions ca. 3000 years earlier. (VOY: "Random Thoughts")
The change was brought on by a Vulcan named Surak, who preached a philosophy of using logic to control emotions, as well as total pacifism. He was effective in spreading his teaching across Vulcan, though he encountered heavy resistance from many Vulcans, especially "those who marched beneath the raptor's wings". A war ensued, and Vulcan was about to "tear itself apart" using weapons like atomic bombs and the Stone of Gol. In the end, the war came to a conclusion and a sizable group of Vulcans eventually left the planet, becoming the ancestors of the Debrune and the Romulans.
Despite Surak's death due to radiation sickness at Mount Seleya shortly before the last battle against "those who marched beneath the raptor's wings", both his katra as well as his writings were preserved in a katric arc and a device called Kir'Shara, respectively. Although both became lost and would not be rediscovered until the mid-22nd century, Vulcan society rose from the ashes by embracing logic and began to rebuild its civilization - a process which took almost 1,500 years.
There is no actual proof that these Vulcans were actually rebelling against Surak; all that is canonically known is that a group of Vulcans left the homeworld around this time, but whether or not they opposed Surak's teachings has never been officially stated on-screen. It is, however, likely that the faction Surak referred to as "those who march beneath the Raptor's wings" were the precursors of the Romulans, given that the Romulan Empire's emblem is a raptor, and their violent, warlike culture.
A deleted scene from ENT: "Chosen Realm" would have established that, even after the embrace of logic, Vulcans continued to war over which exact interpretation from the teachings of Surak was correct. This resulted in a cycle of violence, with one faction trying to suppress another faction, only to find that this was impossible and the other faction eventually retaliating. The cycle was eventually broken by the embrace of non-violence.
In an ultimately omitted line of dialogue from the script for ENT: "Home", it was established that a series of statues overlooking the Fire Plains were built around the Time of Awakening. In the same excised line, T'Pol dated the period as being "more than two thousand Earth years ago" as of 2154 (mid-22nd century), which would date the Time of Awakening to 153 (mid-2nd century) or earlier.
In VOY: "Death Wish", Q claims it was one of Quinn's "self-destructive stunts" that created a misunderstanding which ignited "the hundred-year war between the Romulans and the Vulcans". This war was never further elaborated on, but Q apparently assumed Cpt. Janeway knew about it. It is possible this was intended as a reference to the atomic war following the Time of Awakening.
There are several novels that deal with the Time of Awakening, though revelations in Star Trek: Enterprise's Vulcan Reformation trilogy have rendered them somewhat inconsistent with the Star Trek canon. These include:
- The Romulan Way (Rihannsu #2) by Diane Duane and Peter Morwood
- In this novel the Romulans refer to the Time of Awakening as "The Sundering"
- Spock's World by Diane Duane
- Vulcan's Soul trilogy by Josepha Sherman and Susan Shwartz
- The Yesterday Saga Books #3-5 by A.C. Crispin (canceled)