I found this interesting website (The Art Story) that is an encyclopedia of Modern Artists, Styles & Movements, Timelines, Ideas & Critics, and the Art Story Blog. Based on my knowledge of art and interest in learning about art, it is an excellent website for learning so much more. I see photography as art so this is right up my alley. According to their website the Art Story is:
What is Art Story
The Art Story aims to sort through all the noise of the art world and shed light on modern and contemporary art. Every one of our topic pages is meant to be an analysis that would convince the most ardent skeptic in the value of the particular artist, movement, or idea. This is the mission that we strive for in every single logical argument, artist quote, or supporting resource.
Take a look at The Art Story website and their treatment of Modern Art. I am sure you will think that it is an excellent resource also!