This is a good recorded webinar from NGS/NOAA with an overview of the history of Datum’s for the USA and the future of Datum’s for Mapping and Surveying.  Datums and Projections: Demystifying the Reference Frame

Other great Mapping and Survey Resources and pdf’s to download via NGS/NOAA.  See their Publications website pertaining to the history of Mapping, Surveying, GPS, CORS base stations and Photogrammetry etc.