What makes something "country"?

When we discuss country music (what it was in the 20's), I find it remarkable how different it seems from the country music today. The country music on the radio now really does not seem to have many of the specific qualities that used to make a song, a "country" song. I mean no offense to any country music fans, and you can correct me if I am wrong, but I feel as if many mainstream country musicians out today just sing about cheesy, cliche things, with a southern accent. However, I know that bands do exist out there that seem very similar to how the 20's country was described. I have heard and seen bands with banjos and accordions as their main instruments. If we were following the old musical elements a country band had, these bands would be labeled as "country", but now if anything, they are labeled as something along the lines of "bluesy folk". So, it makes me wonder...what caused this shift? When did country music becomes less related to the "folk" music genre? The country music now, and the country music back then seems very dissimilar. I would love to know when this happened exactly, when the general specifications for being labeled as "country" changed to what they are today Was there a specific reason, like a new musician that changed it?