Progressive Country developed in the late '60s as a reaction to the increasingly polished and pop-oriented sound of mainstream, Nashville-based country. Inspired equally by the spare, twangy, hard-driving sound of Bakersfield country, the singer/songwriter introspection of Bob Dylan, classic honky tonk, and rock & roll, progressive country was the first anti-Nashville movement to emerge since the dawn of rock & roll. Progressive country was rootsier and more intellectual than many of its contemporary genres; it was more concerned with breaking boundaries than with scoring hits. The genre was also songwriter-based. Many of its key artists -- Kris Kristofferson, Willie Nelson, Billy Joe Shaver, Tom T. Hall, Jimmie Dale Gilmore, Butch Hancock -- were not "good" singers by conventional standards, yet they wrote distinctive, individual songs and had compelling voices. By the early '70s, such artists had developed a sizable cult following, and progressive country began to inch its way into the mainstream, usually in the form of cover versions (Sammi Smith took Kristofferson's "Help Me Make It Through the Night" to the country Top Ten). Progressive country also provided the basis for outlaw country, a harder-edged genre that shook country-pop (briefly) off the top of the charts in the mid-'70s. Even after Outlaw's five-year reign in the late '70s, progressive country continued to exist, until it eventually metamorphosed into alternative country in the '80s.