Country Music is American Popular Folk music- originating from the upland hills of the South- i.e. Virginia, Kentucky, and North Carolina- that relies strongly on harmonics, melodies and lyrics for story telling. The Carter Family from Virginia was the first commerical Country Music recording group.
Commercial Country Music has many Pop music elements- as well as Pop music has Country elements- both genres influenced each other. Modern Country and Western originted as we know it by the likes of Hank Williams, Sr. There are many styles and stylists of Country Music- including Country-Pop, Western Swing, Rockabilly, Jazzy Country, New Wave Country, Country-Soul, and Country-Blues. Country Music is essentially song driven- which is why to some non fans describe the songs being too similar. Country Music is actually a very eclectic and broad genre which encompasses folk, rock, and other styles as well. Country Music can be traced back to Celtic music traditions, and has evolved over a period of time . Country Music ranges from a very twangy sound, to a very smooth sound- with much of it in between. Most themes in Country are rural, but it has expanded with mostly songs that simply tell stories- urban or rural. A majority of Country songs have repetition in them and rely heavily on a strong chorus and hooks.
Ironically as traditional as Country Music can be- it has had much innovation and creative influence over the years, and some of the best singers and songwriters of any genre of Popular Music.
When you listen to Johnny Cash, Patsy Cline, and Hank Williams, Sr, you are listening to the roots of Modern Country Music.