Country folk is a term that arose in the mid-1970s when singers took influence from leading folk artists, namely Bob Dylan, and began to write gentler, lyric-based music that incorporated typical country instruments. Some of the earliest and most influential artists that successfully fused these elements include John Prine, Kate Wolf and John Denver. Prine was immediately effective in combining these influences with his eponymous debut album in 1971, containing songs such as Sam Stone which comments on the issue of drug addiction among war veterans. More specifically this has been viewed as a reference to the heroin addiction of soldiers returning from the Vietnam war. A few years later, John Denver released his album Back Home Again which displays some clear country characteristics, especially in the hit songs Thank God I’m a Country Boy and Annie’s Song. The subgenre continued to progress, combining other influences more aligned with country rock however some artists, such as Iris DeMent and Sarah Jarosz, maintain the gentler sound of country folk. The music differs from typical 20th century folk music as it includes instruments such as the mandolin, banjo, fiddle, and steel guitar. Like folk music however, the songs are structurally and harmonically simpler, emphasising the lyrics which are often focused on romantic or social topics.