When Manchester was diagnosed with the illness that would eventually kill him, he took time off from his work on the third volume of Winston Churchill’s life (the volume was eventually completed by another author after Manchester died but it met with lukewarm reviews).  Manchester admits that he started this book based on a fellow authors request for Manchester to write the preface to a history on Magellan, but he found the subject so engrossing that he expanded the preface into this work.  He also admits that he started the book with poor knowledge of the subject which led him to write in an entirely different manner, almost as if he were a graduate student working on his thesis.  He was especially careful of sources and consulted noted historians who specialized in the time period for their input and feedback.