Paul Klee. Wilhelm Worringer's thesis, Empathy and Abstraction (1907) had a large influence on Klee's perspectives on abstract art.
The thesis surfaced that abstract art came about during a period of war. Around three months later Paul returned from Tunis, World War I broke out. Though he had been called to duty in 1916, he wasn't placed in the front line. Meanwhile, he had been successful financially, particularly after a large Berlin exhibition in Der Sturm Gallery. The artist was quite reserved in his remarks concerning the war.