Agrarianism is literally the back to the earth movement. The philosophy is to get people to reject progress, and instead concentrate on the fundamental good of earth, seasons, and simple living. The name Agrarian is most properly applied to the 1920's Agrarian movement, a relatively short lived period which garnered significant notice of the population before extinguishing in the stock market crash of 1929 and the great depression which followed.
Similar movements are recurrent throughout history however; arguably including the 1970's back to the earth movement. These later groups are often referred to as neo-Agrarian.