1) Cubism emerged in the early 20th century, pioneered by Picasso and Braque, breaking from single-point perspective and representing objects from multiple views.
2) Duchamp further challenged notions of art with his "readymades" - mass produced objects designated as art by the artist simply choosing them.
3) Dada emerged during World War 1 as an anti-war movement embracing nonsense and chance procedures. Key figures included Hugo Ball, Tristan Tzara and Hans Arp in Zurich cabarets.