Background: Stephen Arthur Stills (born January 3, 1945) is an American singer, songwriter, and multi-instrumentalist best known for his work with Buffalo Springfield and Crosby, Stills, Nash & Young. Beginning his professional career with Buffalo Springfield, he composed one of their few hits "For What It's Worth," which became one of the most recognizable songs of the 1960s. Other notable songs he contributed to the band were "Sit Down, I Think I Love You
Context: Stills, Furay, and Young reunited in Los Angeles and formed the core of Buffalo Springfield. Legend has it that Stills and Furay recognized Young's converted hearse on the streets of LA and flagged him down, a meeting described in a recent solo track "Round the Bend." The band would release three albums: Buffalo Springfield, Buffalo Springfield Again, and Last Time Around, and enjoy only one hit single, the Stills-penned "For What It's Worth" before disbanding. A Stills song from their debut album, "Sit Down, I Think I Love You," was a minor hit for the Mojo Men in 1967.  During the disintegration of Buffalo Springfield, Stills played on the Super Session album with Al Kooper and joined up with David Crosby, who had recently been ejected from the Byrds in the autumn of 1967. At a party in Laurel Canyon, Crosby was introduced to Graham Nash by a mutual friend, Cass Elliot (formerly of the Mamas and the Papas), and Nash found himself soon joining in singing with Crosby and Stills. Renditions of the latter's "You Don't Have to Cry," led to the formation of Crosby, Stills & Nash. Several of Stills's songs, including "Suite: Judy Blue Eyes" and "You Don't Have To Cry" on the debut album were inspired by his on-again-off-again relationship with singer Judy Collins. In a 1971 interview in Rolling Stone the interviewer noted, "so many of your songs seem to be about Judy Collins." Stills replied, "Well, there are three things men can do with women: love them, suffer for them, or turn them into literature. I've had my share of success and failure at all three."  The cover photo pictured on the debut was taken on the back porch of a house in West Hollywood, which was torn down the next day. Wanting to be able to tour and needing additional musicians, the band invited Neil Young to join them for their subsequent tour and second album to make the group the quartet Crosby Stills Nash & Young.  Having played at the Monterey Pop Festival with Buffalo Springfield, and both Woodstock and Altamont with CSNY, Stills performed at all three of the iconic U.S. rock festivals of the 1960s.
Question: What was the core. Whats the answer?
Stills, Furay, and Young reunited in Los Angeles and formed the core of Buffalo Springfield.