Modernism was a broad movement involving philosophy poetry as well as architecture. I am no expert so I am simply going to quote this brief explanation of Modernism in architecture from Wikipedia:

“Modernist architects and designers, such as Frank Lloyd Wright and Le Corbusier, believed that new technology rendered old styles of building obsolete. Le Corbusier thought that buildings should function as “machines for living in”, analogous to cars, which he saw as machines for traveling in. Just as cars had replaced the horse, so modernist design should reject the old styles and structures inherited from Ancient Greece or from the Middle Ages. Following this machine aesthetic, modernist designers typically rejected decorative motifs in design, preferring to emphasize the materials used and pure geometrical forms. The skyscraper is the archetypal modernist building.”