According to Menzies, some ancient Chinese mariners circumnavigated the globe 70 years before the Portuguese explorer Ferdinand Magellan is recorded as having been the first European to do so in 1519.
In 1999, he began researching the topic, inspired by a statement by the Chinese vice president, Rong Yiren, that a Chinese monk had reached America before Christopher Columbus.
His subsequent publications on the subject generated controversy and criticism from historians, archaeologists, and other academics, who rejected his interpretation of the evidence and sources he presented.
His publications about the topic include 1421: The Year China Discovered the World, 1434: The Year a Magnificent Chinese Fleet Sailed to Italy and Ignited the Renaissance and The Chinese Quest for God.