From a philosophical point of view, what is an art movement?
The apparent explosion of different movements, “isms”, during the 20th century (there must be almost 30 or 40 of them!) was, I think, a side-effect from industrialization, urban congestion, mass media and the intensity of many extraordinary world events. People manifested their thoughts about these events and the most influential manifestations were thus mentioned in the history books and labeled accordingly. Some movements, like “futurism” and “dada”, were directly connected to the world war and must be seen in the light of their contexts to be understood.
Another aspect of the emergence of art movements is artificial and commercial, were producers continuously invent changes to evoke the latest- and the most shocking- “new” in order to maintain their businesses (like in the music-, the design- and the fashion- industries). Since this aspect has disadvantages in that it corrupts immaterial value, movements in fine art are often distinguished by their disinterest in money and objects which could be sold (except for the event itself and the signatures connected to it). Concept art, land art and performance art of various sorts are a few examples.
These are just a few things I come to think of if one would like to understand what an art movement is, before getting entangled in the different manifestos.