The Avars arrived in the Carpathian Basin in the 560s from the steppes of Asia and subdued the Slavs living on the conquered territory. The Avar border run approximately along the line Byzantine Empire in present-day Serbia - Lake Balaton - eastern Bratislava - southern Slovakia - Ruthenia. After the Avars had been defeated at Constantinople in the early 7th century, the Slavs living north of the Danube started to revolt against them. One of merchants delivering arms to the Slavs (mainly) for these revolts was Samo. During a Slav anti-Avar revolt in 623 (probably at today's Bratislava-Devín), Samo joined the Slavs, the Avars were defeated under his leadership, and the Slavs made him their ruler, so that what is known as the King Samo's Empire arose.
Archaeological findings indicate that the “empire” was situated in present-day Moravia, Slovakia, Lower Austria and Carinthia. The settlements of the later Moravian and Nitrian principalities (see Great Moravia) are often identical with those from the time of Samo's Empire. Present-day Bohemia probably, Sorbia at the Elbe surely, and state of Karantania temporarily, became parts of the empire later (in the 630s), as well. The Slavs led by King Samo managed to defeat all Avar attacks, but after the Slavs had killed some Frankish merchants and had stolen some of their commodities, they had to fight against the Franks: In 631, the Frankish king Dagobert I Merovingian (603-639, reigned 629-639) sent three armies against King Samo. One of the armies - the biggest one from Austrasia (Avstrazia) - was defeated by the Slavs led by King Samo at the (today unknown) castle Wogastisburg (Vosgate Castle) when trying to attack the center of Samo's Empire. As a result, Samo even invaded Frankish Thuringia several times and undertook looting raids there. The Sorbian prince Dervan joined Samo after this success. The location of the Wogastisburg is still strongly disputed (castles in Bohemia, castles at the Danube, the Frankish Forchheim, Bratislava, Carnuntum etc.).
The history of the empire after Samo's death in 658 (some sources: 659) are 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 Slovakia) and entered into a symbiosis with the Slavs, whereas territories to the north of the Avar empire were purely Slav territories. The first particular thing that is known about the fate of these Slavs and Avars, is the existence of the Moravian and Nitrian principalities in the late 8th century (see Great Moravia) which were attacking the Avars, and the defeat of the Avars by the Franks under Charlemagne in 799 or 802/803, after which the Avars quickly ceased to exist.
The main source of written information on Samo and his „empire“ is the Frankish Fredegarii Chronicon (Fredegar's Chronicle). It has been written by one author (maybe called Fredegar) around 660 or by three authors in the first half of the 7th century. Its second part describes the history of the Franks between 584 and 642/643 and is one of the main source on the history of the Frankish historz. It is the only contemporaneous source on Samo. All other sources are derived from this chronicle and are much younger. Examples of such sources are the Gesta Dagoberti I. regnis Francorum from the first third of the 9th century, and the Conversio Bagoariorum et Carantanorum (Conversion of the Bavarians and Karantanians) from 871-872 from Salzburg (the center of Bavarian clergy) , the latter being a very tendentious one as its name suggests (which however does not mean necessarily that it is wrong). According mainly to the Conversio, Samo was a Karantanian merchant.
See also: Timeline of Slovene history, History of the Czech Republic, History of Slovakia.