Abstract Expressionism developed in New York in the 1940’s during the post WWII movement.
Kandinsky and Mondrian were forerunners of Abstract Expressionism, freeing themselves from the portrayal of objects by attempting to evoke emotions and feelings from the viewer. Abstract Expressionism was an important predecessor of Surrealism, aiming to draw the viewer deep into the subconscious mind with paintings created unconsciously and spontaneously, depicting raw emotion, expressive and with action.
The emphasis was definitely on the spontaneous, automatic and subconscious creation. To express oneself through the use of form and colour in a non-representational, non-objective style.
Abstract Expressionism can be divided into two groups.
Action Painting, sometimes known as Gestural Abstraction was as the name suggests, a more gestural abstraction typified in the work of Pollack, Kline and Guston, stressing the physical action of painting and exploitation of accidental effects in large gestures and expressive painting.
Tachism, sometimes known as Colour Field Painting, was the European equivalent of Abstract Expressionism. Less aggressive and abandoning geometric abstraction in favour of a more intuitive form of expression. Examples of Tachism through the work of artists such as Rothko and Noland, especially concerning the exploration of effects of pure colour on a canvas.
Sources:
OCA Painting 1 Learning Log 