This is an interesting PBS documentary on the evolution of farming, implements, and then, tractors. A lot of history about McCormick, Deering, John Deere, Fordson, and some brands I'd never heard of. Also interesting is the total absence of mentioning Best/Holt/Caterpillar. Perhaps it was because the documentary focusses mainly on the midwest and those brands hadn't established themselves in that part of the country yet.
Either way, it's pretty interesting and well done.