Europe's Forgotten Medieval Empire (c. 626 - 658 AD)

6 months ago, I stumbled onto a wiki page for one "King Samo", a 7th century ruler of a tribal military confederation in central europe (modern Czechia, Slovakia, Austria, Hungary, Germany, etc). They revolted and defeat the Avar Khaganate, they fought and defeated King Dagobert I and his Frankish army at Wogastisberg. How, HOW had I not heard of this? This is the story of Samo's 'Empire', the Chronicle that records his exploits, and its place in 'dark age' European history.