All other sources for Samo are derived from Fredegar, and are much more recent. The Gesta Dagoberti I regnis Francorum ("Deeds of King Dagobert I of the Franks") was written in the first third of the ninth century. The Conversio Bagoariorum et Carantanorum ("Conversion of the Bavarians and Karantanians") from Salzburg (the Bavarian ecclesiastic centre), written in 871–872, is a very tendentious source, as its name suggests. According mainly to the Conversio, Samo was a Karantanian merchant.
The sources "Fredegar" used to compile his Wendish account are unknown. A few scholars have attacked the entire account as fictitious, but Fredegar displays a critical attitude and a knowledge of detail that suggest otherwise. It is possible that he had an eyewitness in the person of Sicharius, the ambassador of Dagobert I to the Slavs. According to Fredegar, the "Wends" had long been subjects and befulci of the Avars. Befulci was a word, cognative with the word fulcfree found in the Edict of Rothari, signifying "entrusted [to guard]", from the Old German root felhan, falh, fulgum and Middle German bevelhen. Fredegar appears to have envisaged the Wends as a military unit of the Avar host. He probably based his account on "native" Wendish accounts. Fredegar records the story of the origo gentis (origin of the people) of the Wends. The Wends were Slavs, but Samo was only king of the Wends, at least in Fredegar's eyes.
It has also been suggested that Fredegar's sources may have been the reports of Christian missionaries, especially disciples of Columbanus and the Abbey of Luxeuil. If this is the case, it may explain why he is remarkably free of typical stereotypes of heathen Slavs: he was familiar with the Wends as a specifically pagan nation.
The most famous event of Samo's career is his victory over Frankish royal army under Dagobert I in 631 or 632. Provoked to action by a "violent quarrel in the Pannonian kingdom of the Avars or Huns" during his ninth year (631–2), Dagobert led three armies against the Wends, the largest being composed of Austrasians under himself. The Franks were routed near Wogastisburg (Latin castrum Wogastisburc), an unidentified location meaning "fortress/castle of Vogast." In the aftermath of the Wendish victory, the Sorbian prince Dervan abandoned the Franks and "placed himself and his people under Samo" (Fredegar). Samo even invaded Frankish Thuringia several times and undertook looting raids there.
In 641 the rebellious duke of Thuringia, Radulf, sought an alliance with Samo against his sovereign, Sigebert III. Samo also maintained long-distance trade relationships. On his death, however, his title was not inherited by his sons. Ultimately, Samo can be credited with forging a Wendish identity by speaking on behalf of the community which recognised his authority.
The history of the empire after Samo's death in 658 or 659 is largely unclear. It is generally assumed that it disappeared with Samo's death. Archaeological findings show that the Avars returned to their previous territories (at least to southernmost part of present-day Slovakia) and entered into a symbiosis with the Slavs, whereas territories to the north of the Avar empire were purely Slav territories. The first specific thing that is known about the fate of these Slavs and Avars, is the existence of the Moravian and Nitrian principalities in the late eighth century which were attacking the Avars, and the defeat of the Avars by the Franks under Charlemagne in 799 or 802–3, after which the Avars quickly ceased to exist.