Cubism popped up in 1907 with funny houses near Marseille ("l'Estaque") and presentation of multiple views of the same object in the very flat space of the picture. The Cubists always claimed to be realists.
Cubist presented a new reality in paintings.
The most radical attempt to enforce one reading of the picture - that of a man-made construction.
Cubism means modern art from the beginning of the 20th century not knowing what does it mean modern art painting.