John Toland, 91, the author and historian who wrote a best-selling biography of Adolf Hitler and won a Pulitzer Prize for his description of the Japanese Empire in the 1930s and '40s and the events that led it into war against the United States, died of pneumonia Jan. 4 at Danbury Hospital in Connecticut.

Mr. Toland also wrote a book about the Japanese attack on Pearl Harbor on Dec. 7, 1941, arguing that President Franklin D. Roosevelt and top government leaders knew about it in advance but did nothing to stop it because they wanted war with Japan. This theory -- the subject of widespread speculation since shortly after the attack -- was roundly denounced by several historians and journalists.

"It simply doesn't wash," Washington Post chief diplomatic correspondent Chalmers M. Roberts wrote in a 1982 review of Mr. Toland's book "Infamy: Pearl Harbor and Its Aftermath."

As a historical storyteller, Mr. Toland based his narratives on hundreds of interviews with participants in the events about which he wrote and then attempted to describe the unfolding of history from as many sides as possible, as well as its impact on the famous and the ordinary.

In his Pulitzer Prize-winning book "The Rising Sun: The Decline and Fall of the Japanese Empire, 1936-1945," published in 1970, he talked with high-ranking Japanese military officers, low-ranking enlisted men, government officials, diplomats and housewives who survived the atomic bombings of Hiroshima and Nagasaki.

Mr. Toland described his book as "a factual saga of people caught up in the flood of the most overwhelming war of mankind, told as it happened -- muddled, ennobling, disgraceful, frustrating, full of paradox," the Associated Press reported. William Craig of The Washington Post's Book World wrote that "nowhere in American literature has the Japanese side of the war in the jungles been so well told. . . . Toland has fashioned a compelling portrait of Japan at the brink of national suicide."

Mr. Toland said he spent six years in Japan researching material for "The Rising Sun." He went there, he said, with a dislike for the Japanese because of their conduct during the war but then ended up writing the book to explain why they behaved as they did. "You don't have to take sides. All you have to do is get people's motivations," he told the Associated Press.

In Tokyo, Mr. Toland met Toshiko Matsumura, an English-speaking Japanese woman who was a correspondent for McGraw-Hill World News. He hired her to be his interpreter. In 1960, they were married.

For his biography of Hitler, published in 1976, Mr. Toland interviewed 200 people who worked with or knew the Nazi leader. "Toland tells us more about Hitler than anyone knew before," Peter S. Prescott wrote in Newsweek.

Journalist Ted Morgan wrote in The Washington Post that a subtitle for Mr. Toland's Hitler biography could well have been "Everything You Always Wanted to Know about Hitler and Were Afraid to Ask":

"No, Hitler did not have an undescended testicle. Yes, Hitler's hatred of the Jews may have been based in part on his mother's death from cancer after having been treated with a useless drug called iodoform by a Jewish doctor. Yes, it is possible that he had a Jewish grandfather. No, Hitler was not a homosexual. . . . "

Had Hitler died in 1937, two years before World War II started, Mr. Toland wrote, "he would undoubtedly have gone down as one of the greatest figures in German history." He unified Germany, brought about a Nazi New Deal, persuaded Ferdinand Porsche to design a people's car that became the Volkswagen, and ordered factories in the Rhur to install antipollution devices.

John Toland was born in La Crosse, Wis. He graduated from Williams College, attended Yale Drama School and served six years in the Army Air Forces.

But his early years as a writer were a disaster. "I was about as big a failure as a man can be," Mr. Toland told The Washington Post in 1961. He had written, he said, about 25 plays, six novels and 100 short stories, none of which sold. He ran a gift shop that failed and a dance studio that bored him. Finally in 1954, at the age of 42, he sold a short story to American Magazine. He was paid $165.

His first book, "Ships in the Sky," published in 1957, was about dirigibles.

Of all Mr. Toland's writings, none triggered the controversy provoked by "Infamy," the book about the Pearl Harbor attack. In that book, Mr. Toland wrote that Roosevelt, Gen. George C. Marshall, Adm. Harold R. Stark and others constituted "a small group of men, revered and held to be most honorable by millions, who had convinced themselves it was necessary to act dishonorably for the good of their nation -- and incited the war that Japan had tried to avoid."

Disputing this theory, Roberts wrote in The Post that Mr. Toland's "thesis depends on a collection of unverifiable conversations, lapses in memory, uncertain memoranda and fragmentary messages. . . . "

Mr. Toland's other books included a novel about World War II, a history of the last year of World War I, an account of the Battle of the Bulge and a book about the 1930s gangster John Dillinger. In 1997, he published an autobiography, "Captured by History: One Man's Vision of Our Tumultuous Century."

Mr. Toland's marriage to Dorothy Toland ended in divorce.

Survivors include his wife, Toshiko, of Danbury; their daughter, Tomiko; two daughters from his first marriage, Diana and Marcia; and three grandchildren.