William R. Polk, a longtime historian, diplomat and noted Middle East scholar who helped negotiate resolutions to several conflicts, including the 1967 Arab-Israeli War, died on April 6 at his home in Vence, in southeast France near the Mediterranean Sea. He was 91.

His daughter Milbry Polk said the cause was leukemia.

Over six decades, Mr. Polk delved into multiple careers, working in and out of government, writing, co-writing or editing more than two-dozen books and traveling the globe, often to hot spots.

His academic background was in Middle East studies. In the late 1950s, he started writing articles in The Atlantic, Foreign Affairs and other publications detailing what he saw as the failures of American policy in the region. In 1961 President John F. Kennedy put him in charge of planning policy for most of the Islamic world.

He also served on Kennedy’s three-man “crisis management committee” during the Cuban Missile Crisis.