Time of Awakening
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.
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", even starting a nuclear war. Surak died of radiation sickness shortly before the last battle against these factions, but his writings were preserved in the Kir'Shara.
In the end, a sizable group of Vulcans eventually left the planet, becoming the ancestors of the Debrune and the Romulans.