The Whitney Museum of American Art - known informally as the "Whitney" - is an art museum located in Manhattan. It was founded in 1931 by Gertrude Vanderbilt Whitney (1875-1942), a wealthy and prominent American socialite and art patron after whom the museum is named. The Whitney focuses on 20th- and 21st-century American art. Its permanent collection comprises more than 21,000 paintings, sculptures, drawings, prints, photographs, films, videos, and artifacts of new media by more than 3,000 artists.

Gertrude Vanderbilt Whitney, the museum's namesake and founder, was herself a well-regarded sculptor as well as a serious art collector. As a patron of the arts, she had already achieved some success as the creator of the "Whitney Studio Club", a New York-based exhibition space which she created in 1918 to promote the works of avant-garde and unrecognized American artists. Whitney favored the radical art of the American artists of the Ashcan School such as John Sloan, George Luks and Everett Shinn, as well as others such as Edward Hopper, Stuart Davis, Charles Demuth, Charles Sheeler, and Max Weber.  With the aid of her assistant, Juliana R. Force, Whitney had collected nearly 700 works of American art. In 1929, she offered to donate over 500 works of art to the Metropolitan Museum of Art, but the museum declined the gift. This, along with the apparent preference for European modernism at the recently opened Museum of Modern Art, led Whitney to start her own museum, exclusively for American art, in 1929.  Whitney Library archives from 1928 reveal that during this time the Studio Club utilized the gallery space of Wilhelmina Weber Furlong of the Art Students League to exhibit traveling shows featuring Modernist works. In 1931, architect Noel L. Miller converted three row houses on West 8th Street in Greenwich Village - one of which had been the location of the "Studio Club" - to be the museum's home as well as a residence for Whitney. Force became the first director of the museum, and under her guidance, the museum concentrated on displaying the works of new and contemporary American artists.  In 1954, the museum left its original location and moved to a small structure on 54th Street connected to and behind the Museum of Modern Art on 53rd Street. On April 15, 1958, a fire on the second floor of MOMA that killed one person forced the evacuation of paintings and staff on MOMA's upper floors to the Whitney. Among the paintings moved in the evacuation was A Sunday Afternoon on the Island of La Grande Jatte which had been on loan from the Art Institute of Chicago.

Answer the following question by taking a quote from the article: How did the museum begin?
she offered to donate over 500 works of art to the Metropolitan Museum of Art, but the museum declined the gift.