"modern" is sort of like with tractors. I refer to "modern" to mean the basic high arm shape that we got use to seeing. So many of the earlier ones look quite different. It just so happens that this "look" that lasted came into being around 1890 or so . . .
"Modern" tractors are considered to be those with live PTO, hydraulics and three point hitch - which came into use around late 50's, early 60's. So my 1963 Oliver is considered a "modern" style tractor. Proir to that tractors came with some interesting styles, hitch methods and other options. After that point, they were a lot more "standardized".