The "extinction period" (also called the "extinction event") was an event that began around the start of the 1976 military coup d'état and fade away with its collapse around 1983, during this time the supernaturals in Buenos Aires, and by minor extent those in other regions of Argentina, endure an unyielding and merciless persecution by hunters align with the new military government. The slaughter that was seen in Buenos Aires was like no other and most of their members either died or escaped to other countries, those who managed to hide from the slaughter would have to endure being in total isolation for 7 years. Most of the persecution carried out against the civilian population was also carried out against any suspected supernatural being present in Buenos Aires, some groups lost most of their hierarchy and were left totally blind and with out guidance, while others were targeted by association and other saw an estrange rise in their population during this time.
Most supernatural elders and historians argue that in reality the plans for this mas execution were laid out much before this time, which most agree that the events that transpired happened as a result of supernatural meddling in mortals affairs, mostly by proxy as provocation after varios mass persecutions of civilians had taken place before, and the fact that most supernaturals have, in some or another, a connection with mortals and weren't too keen in just sit and turn a blind eye while family, friends and territory where all burned to the ground. An Uratha pack who's loci was about to get defiled by government agents and that to prevent it they decided to go toe to toe against them, a Carthian Vampire who was in amicable terms with a Peronist political group of students that were attacked and captured during a protest decided to take a leap and to try liberating them, a Changeling who's family is threaten by government forces due to their political alignment, or just because the hell of it, decided to use all resources they have to protect them. This incidents and more like them lead to the eventual discovery by government forces of the supernatural world that lurked under the shadows of Buenos Aires. By the time the foundation laid out by the Revolución Libertadora came crumbling down the military traitors somewhat knew what they were facing against and started planing a way to eliminate this new threat that had appear.
When Peron died and a new coup was approaching, the military hunters had already laid a solid plan and made a copule of alliances that would ensure their victory and total hegemony of their power.