Egyptian chronology
There are differences between the two sets of dates because of new discoveries and a better understanding of what is already known. For example, in Breasted's 1906 list, he added a ruler in the Twentieth dynasty that further research would show did not exist. Using Manetho writings, Breasted also believed that each new dynasty followed the old one in a sequence. It is now known that several dynasties existed at the same time. Those changes changed the chronology by 400 years at the beginning of Dynasty I.