Country music was always a part of Rock and Roll. It was there in Elvis Presley's work, just as it was present in the southern Soul of the 1960s and in Chuck Berry's "Maybellene." The Beatles played with it, as did the Rolling Stones. Without that Country ingredient, Rock and Roll would be different. Thus, in many ways, Country Rock was nothing new when it came along in the late 1960s and 1970s. What it did that was different, however, was to foreground the Country element in ways that were new to the Rock and Roll world.
Country Rock and Folk Rock, however different, share some tendencies. Both genres work the soil of the past in order to cultivate the next musical scene. Gram Parsons, one of Country Rock's most significant but also most mythologized figures, due in part to an early death and the mystery surrounding it, was overt in his sense that the past held the key. His song "Older Guys" (co-written with Chris Hillman and Bernie Leadon), if operating at a few levels, has what might be called his cornerstone belief: "The older guys really got it all worked out." Parsons did indeed draw from the worlds of Hank Williams, Ernest Tubb, and others to create his own version of Country. But as a short-term member of the Byrds and a part-time member of the Rolling Stones' entourage, Parsons was indeed bringing two things together.
Country Rock, extending from Parsons' work with the Byrds on Sweetheart of the Rodeo and his band Flying Burrito Brothers up through the early recordings of the Eagles, Poco, and others, was a part of the wider youth culture of the 1960s. It was the sound of young people looking for the cultures that felt more "real" than what they were finding on their doorsteps. Of course, as a tendency, this reaching into Country's history in order to find something fresh and viable extends well beyond Country Rock. From Elvis Costello's Almost Blue to the whole of the "Alt Country" scene, it's a thing that has been happening for some time and will likely not run its course any time soon.