Gertrude Vanderbilt Whitney announced the founding of the Whitney Museum of American Art in January 1930, but her support of artists from the early 1900s until her death in 1942, her abiding concern to aid living artists from the United States had begun more than twenty years earlier. As a sculptor in the academic tradition, she realized that there were few opportunities for independent artists to exhibit or sell their works, especially those from the United States. She remained the greatest patron of art of the twentieth century. As early as 1907, Whitney organized an exhibition of contemporary art in the United States for the Colony Club, a women's club in New York City of which she was a founding member. The following year she purchased four of the seven paintings sold from the landmark exhibition of 'The Eight' at the Macbeth Galleries. She contributed funds to the Armory Show of 1913, and for many years paid her deficit of the society of Independent Artists, founded in 1917. In 1914, Whitney converted a townhouse into a small gallery known as the Whitney Studio, which featured regular exhibitions of the work of artists from the United States. In 1918, she established the Whitney Studio Club: any artist introduced by a member could join the club, where annual exhibitions gave members a rare opportunity to present their works to the public without first submitting them to a jury. She aided artists in numerous other ways--sending them abroad to study, paying their hospital bills and studio rents, and most important, purchasing their works. By 1929, Whitney owned more than five hundred works by artists from the United States, and she felt the public should have an opportunity to see the collection. That year she offered the collection to the Metropolitan Museum of Modern Art, whose director refused her offer before she even had a chance to express her intention to build and endow a Whitney wing. This abrupt rejection only served to challenge Whitney, who announced in January 1930 that she would establish her own museum with a new and dramatically different mandate--to support artists from the United States. What is the main topic of the passage?