Otto Dix is a very important inter-war and post war German artist. He served in the trenches and a lot of his art covers the horror of WW1. The Nazis did not like him and made him paint landscapes which he still managed to fit anti-nazi motifs into.

One interesting way to approach the subject would be to look into the trend of post-war art for all the Axis Powers for context. There was a fantastic show from the Rachofsky Collection over post-war Italian and Japanese works. The Guggenheim also had a retrospective for the Gutai Group just last year.

During Japanese reconstruction for the following years after the end of the war, the quick bloat of the consumer-class and the quick abandonment of Imperial ideal in favor of more western-focused attitudes led a significant shift in demographic of art-makers-- namely, the trained and prestigious court gentry painters of, say, the Edo period were replaced with a caustic and empowered youth who turned their gazes to the West, particularly the contemporaries Georges Mathieu and Jackson Pollock. These young artists (established as the to-be incredibly influential "Gutai Group" in 1954) were actively engaged in performative painting and installation, embracing dialogue between the artist and the raw material. Artists like Saburo Murakami, Shozo Shimamoto, etc. engaged with the canvas in performative ways by pouring, throwing, slipping through paint with their feet, even running through canvas. Borne of a new generation of consumers looking to rid themselves of the (seen-as) antiquated imperial system, the Gutai Group would go on to interact with the art world on a global scale, informing the soon-to-develop Fluxus movements as well as the Conceptual and installation artists in the West.

Italy's drastic transformation in art, on the other hand, arose primarily from the quick economic and political collapse that followed the end of the second World War. One of the really interesting things here is the use of these traditional materials and images that had been historically grounded to Italy (marble and bronze especially) in these ways that essentially sought to overturn the previous establishments that had been prevalent in the country. One of the significant movements coming out of Italy in this time of radical instability would be Arte Povera.

I know that Germany experienced a quick turn towards contemporary art, Western Germany becoming a fairly established producer of Conceptualists in the 60's and 70's. Examples include Hanne Darboven and Gerhard Richter.

One of the key recurring themes in these regions is the reactionary shift away from tradition and "antiquated" ideal, mostly arising from the desire to culturally distance oneself from the past following a conflict as intense and as gravely somber as World War II. As a result, a new class of avant-garde popped up over night, disillusioned with the past conflict and looking to push forward into a new and fresher form of art.

Further Reading: Packet over Rachofsky Exhibition, featuring the essays of the founders of some of the avant-garde movements, as well as overviews:

Technical Manifesto[excerpt], Lucio Fontana, 1951

Free Dimension, Piero Manzoni, 1959

Arte Povera-- Im Spazio, Germano Celant, 1967

The Gutai Manifesto, Jiro Yoshihara, 1956

Foreshadowings and Premonitions: Mono-Ha, Lee Ufan, 2001