I found this series to be very attractive, beautifully designed, but somewhat weak on substance.  The binding is sturdy, the cover is shiny, the text is interspersed with attractive photos and illustrations, and vocabulary words are defined in the margins.  All of these are nice features.  But I thought the information was somewhat lacking in depth.  Right away in the first chapter it tells us that modern historians must rely on archaeology and the written accounts of Spanish invaders and native Incas who were educated by those invaders after the 1500s, because the Inca people left no written records. The author even uses the words “cloaked in mystery” to describe the early history, but then the text goes on to assert as fact many details from ancient times without ever backing up for the reader how we know what we think we know.  I would have liked to have seen more frequently phrases such as, “[such and such] evidence indicates…”  Also, the designers of the book are guilty of one of my current pet-pieves for non-fiction text features:  a “timeline” that is really just a sequence of events written horizontally, where dates are evenly spaced without regard to how much time separated them:  two inches in one place represents 500 years, and in another place along the same line, the same two inches represents only 25 years.  In elementary school, I was taught that the distance along a timeline was supposed to be a visual representation of actual time.