Abstract Expressionism is the term used for new forms of abstract art coming from American painters such as Jackson Pollock, Mark Rothko, and Willem de Kooning in the 1940s and 1950s.

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The Origins
One of the many paradoxes of Abstract Expressionism is that the origins of the movement can be traced back to the figurative painting of the 1930s. Almost all the artists who would later become abstract artists in New York were influenced by the experience of the Great Depression. They became mature whilst painting in styles influenced by Regionalist movements.
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Abstract Painting Features
Abstract Expressionism is famous for large-scale works distant from traditional processes. While Abstract Expressionism is studied for its advancements in painting, its ideas had a deep influence in many aspects of everyday life, including drawing and sculpture. Similarly, instead of having an interest solely in finished works, these artists focused on the process.
The shapes are employed in various ways to create a sensation of volume, and movement. These elements are fused into expressive patterns in order to depict real or supernatural phenomena.

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The Most Important Painters
Here are the names of the best-known artists of this movement:
- Paul Klee: he was a Swiss artist famous for his large body of works influenced by Cubism, Expressionism, and Surrealism;
- Piet Mondrian: he was a Dutch painter, leading figure in the De Stijl movement, that focused on simple forms and colors,
- Hans Arp: he was one of the main artists of Dada in Zurich;
- Malevich: Russian artist that will found Suprematism.
- Robert Delaunay: he was the author of the “Sun and the Moon” (1912), “Sun n. 2” (1912-1913), “The City” (1910).

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Info source: https://www.britannica.com/art/abstract-art