The Ahkh was a time of conflict that raged before the Vulcan Reformation and the Sundering.
This period in Vulcan's history was an intense war between the Vulcan people and the Duthulhiv pirates that descended upon their world. It was declared after the initial meeting was made between Vulcan dignitaries and the "aliens" where the Orion forces attacked the inhabitants viciously. This act resulted in what Vulcans referred to as "the" War, relegating all previous conflicts to mere tribal feuds and unified the world against this new threat to all Vulcans.
During the conflict, psi-talents were used that caused ships to fall apart, alien pilots getting locked into suicidal courses and the destruction created being sent to the worlds of Duthul and Etosha which clearly stated that all future invaders would face death.
The time of the Ahkh would form a future schism in Vulcan society as it convinced Surak's student, S'task, that pacifism would not protect them from the universe around them. This schism brought about an exodus from many Vulcans that would later form the Romulan race. (TOS novel: Spock's World)