American modernism, like modernism in general, is a trend of thought that affirms the power of human beings to create, improve, and reshape their environment, with the aid of scientific knowledge, technology and practical experimentation, and is thus in its essence both progressive and optimistic.[citation needed] American modernism is an artistic and cultural movement in the United States starting at the turn of the 20th century with its core period between World War I and World War II and continuing into the 21st century