Visually depicted in part in the ["YO OSI" segment of The Invisible Hand of Fate Pyramid Wars of 1987 was a war in the fictional universe of the Venture Bros. between the Office of Secret Intelligence and the terrorist organization S.P.H.I.N.X.. The event resulted in the victory of the OSI and the destruction of SPHINX.
Known casualties of the war include a man with a gold-plated head that looks like Destro from GI JOE. S.P.H.I.N.X. Commander, Wind Song, Diamond Backdraft, and the Countess all survived the war. 
The first legacy left behind from the war was its equipment. Following the defeat of the original SPHINX, the OSI took possession of most of its technology and gear, such as the Mighty Khafra. Decades later, Hunter Gathers and a number of other disaffected ex-OSI operatives, sick of the bureaucratic red tape that burdened the OSI, adopted the SPHINX identity and commandeered its equipment. This group was an entirely new group with a different purpose: vigilante justice to evildoers who didn't play beyond the rules of organized villainy set by the Guild of Calamitous Intent. Following the readmission of Gathers and co. to the OSI, SPHINX was abandoned by everyone save for Henchman 21, whom was never an OSI agent to begin with.
The second legacy of the war was the surviving agents of SPHINX going into hiding and/or assuming normal civilian lives to blend in with the populace. However, they still held grudges against the OSR in their hearts. They also knew one day that the chip planted in their skulls to keep them loyal would eventually fail and leak poison into their system, killing them. Therefore, when Henchman 21 issued a call for new SPHINX members, SPHINX Commander, Wind Song, and Diamnond Backdraft all came in and infiltrated his group shortly before taking it over from him. Together, they took the Mighty Khafra and made a suicide run to take OSI down in a final blaze of glory. However, their efforts were ultimately scuttled.