https://en.wikipedia.org/wiki/Kingdom_of_Northumbria
https://www.ericschumacher.net/blog/2018/7/29/harald-bluetooth-the-builder-king
https://www.youtube.com/watch?v=gTC44GnX7Qk&
https://en.wikipedia.org/wiki/Gorm_the_Old
https://en.wikipedia.org/wiki/Jelling_stones
https://en.wikipedia.org/wiki/Viking_ring_fortress
https://norse-mythology.net/who-was-harald-bluetooth/
https://en.wikipedia.org/wiki/Harald_Bluetooth
https://www.thoughtco.com/harald-bluetooth-profile-1788985
https://www.britannica.com/place/Denmark/The-Viking-era
https://en.natmus.dk/historical-knowledge/denmark/prehistoric-period-until-1050-ad/the-viking-age/religion-magic-death-and-rituals/the-transition-to-christianity/
http://www.dandebat.dk/eng-dk-historie19.htm
https://www.bluetooth.com/about-us/bluetooth-origin/
https://www.huffpost.com/entry/why-called-bluetooth_l_5cdd7c62e4b01571365d568a