New Defender's Study Bible Notes
6:1 four hundred and eightieth year. This is a key verse in establishing the Biblical chronology of world history, particularly the chronology of the period of the judges. The other chronological data given in the books of Joshua, Judges and Samuel, however, have been difficult to fit into this framework (though numerous harmonizations have been proposed). There may well have been occasions when the tenures of certain judges overlapped with each other or with the periods of oppression as listed in Judges, so that it would be impracticable simply to add up all the numbers as listed. This verse has perhaps been inserted, under the inspiration of the Holy Spirit, for the specific purpose of providing the over-all chronology which would otherwise be impossible to obtain with certainty.
However, secular archaeologists dispute the Biblical chronology, as well as the events associated with it. The problems of correlating the events of the exodus and conquest with secular chronology have not yet been fully resolved, but the many uncertainties in secular dating methods certainly do not warrant confidence in them. We can be sure the Biblical record is fully reliable, and will eventually be fully validated.