From MoMA Learning

(Museum of Modern Art, New York)

The early 1960s brought a significant shift in American art, largely in reaction to the critical and popular success of the highly personal and expressive gestures of Abstract Expressionist painting. Minimalist artists produced softened three-dimensional objects, freed from representational content.

Their new vocabulary of simplified, geometric forms made from modest industrial materials such as fiberglass and aluminum, and often using mathematical systems to determine the composition of their works, challenged traditional notions of craftsmanship, the illusion of three-dimensionality, or spatial depth, and the idea that a work of art should be unique in its kind.   

Source: https://www.moma.org/learn/moma_learning/themes/minimalism/