Human history up until about a hundred years ago was totally open to somebody doing oh i don't know some sort of a raid on a fabulously rich area that was just beckoning people to come and take stuff. In the modern age you don't need very long to respond which is why the last hundred or so years is a bit different in laguna beach they would have known about five viking ships approaching the coast long before they got anywhere near the coast.
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.