Michener was a popular writer during his lifetime; his novels sold an estimated 75 million copies worldwide. His novel "Hawaii" (1959), well-timed on its publication when Hawaii became the 50th state, was based on extensive research. He used this approach for nearly all of his subsequent novels, which were based on detailed historical, cultural, and even geological research. "Centennial" (1974), which documented several generations of families in the Rocky Mountains of the American West, was adapted as a popular 12-part television miniseries of the same name and aired on the National Broadcasting Company (NBC television network) from October 1978 through February 1979.