New York ? Susan Sontag, a leading intellectual and activist of the past half-century who introduced the concept of “camp” to mainstream culture and also influenced the way many thought about art, illness and photography, died Tuesday. She was 71.

Sontag died at 7:10 a.m., said Esther Carver, a spokeswoman for Memorial Sloan-Kettering Cancer Center in Manhattan. Her son, David Rieff, said the cause was complications of acute myelogenous leukemia, one of the deadliest forms of leukemia.

She wrote a best-selling historical novel, “The Volcano Lover,” and in 2000 won the National Book Award for the historical novel “In America.” But her greatest literary impact was as an essayist.

Her 1964 piece, “Notes on Camp,” which established her as a major new writer, popularized the “so bad it’s good” attitude toward popular culture, applicable to everything from “Swan Lake” to feather boas. In “Against Interpretation,” this most analytical of writers worried that critical analysis interfered with art’s “incantatory, magical” power.

She also wrote such influential works as “Illness as Metaphor,” in which she examined how disease had been alternately romanticized and demonized, and “On Photography,” in which she argued pictures sometimes distance viewers from the subject matter. “On Photography” received a National Book Critics Circle award in 1978. “Regarding the Pain of Others,” a partial refutation of “On Photography,” was an NBCC finalist in 2004.

Unlike many American authors, she was deeply involved in politics, even after the 1960s. From 1987-89, Sontag served as president of the American chapter of the writers organization PEN. When the Ayatollah Ruhollah Khomeini called for Salman Rushdie’s death because of the alleged blasphemy of Rushdie’s “The Satanic Verses,” Sontag helped lead protests in the literary community.

“She was a true friend in need,” Rushdie said in a statement Tuesday. “Susan Sontag was a great literary artist, a fearless and original thinker, ever valiant for truth, and an indefatigable ally in many struggles.”

Sontag’s fiction became more accessible. She wrote an acclaimed short story about AIDS, “The Way We Live Now,” and a best-selling novel, “The Volcano Lover,” about Lord Nelson and his mistress, Lady Hamilton.

In 2000, her novel, “In America,” about 19th-century Polish actress Helena Modjeska, was a commercial disappointment and was criticized for the uncredited use of material from fiction and nonfiction sources. Nonetheless, Sontag won the National Book Award.

In 1999, she wrote an essay for “Women,” a compilation of portraits by her companion, photographer Annie Leibovitz.

Sontag did not practice the art of restrained discourse. Writing in the 1960s about the Vietnam War she declared “the white race is the cancer of human history.” Days after the 9-11 terrorist attacks, she criticized U.S. foreign policy and offered backhanded praise for the hijackers.

“Where is the acknowledgment that this was not a ‘cowardly’ attack on ‘civilization’ or ‘liberty’ or ‘humanity’ or ‘the free world’ but an attack on the world’s self-proclaimed superpower, undertaken as a consequence of specific American alliances and actions?” she wrote in The New Yorker.