As I see it, all of them - Tachists, Action Painters, Informel artists, and the rest - are only part of an Informel movement that covers a lot of other things as well. I think there's an Informel element in Beuys, as well; but it all began with Duchamp and chance, or with Mondrian, or with the Impressionists. The Informel is the opposite of the constructional quality of classicism - the age of kings, or clearly formed hierarchies.
Gerhard Richter, Dietmar Elger, Hans-Ulrich Obrist (2009). “Gerhard Richter: writings 1961-2007”, Distributed Art Pub Inc