During the Viking age Denmark was not a unified kingdom or state of any kind. The Danish kings during this era will fortify and perhaps expand an already existing fortification which separated sort of the territory of the Danes from that of the Saxons. By about this time your history books are going to start labeling this entire era as the Viking age.
This show picks up where Dan's Thor's Angels show left off. In the early Middle Ages Pagan Germanic-language speakers like the Vikings are a dying breed. Many of their contemporaries wish they'd die faster.