The Longobards left the Carpathian Basin for Northern Italy after the invasion of the territory by the Avars in 568. The Avars were a group of nomadic warriors of mixed origin. They conquered the Carpathian Basin, subjugated the local peoples and launched plundering expeditions against the neighboring powers during the next decades. By the time of the Avars' arrival, the Slavs had settled in most lands that now form Slovakia, according to historian Stanislav Kirschbaum. Further migration waves strengthened the local Slavic population because new Slavic groups, pressed by the Avars, crossed the Eastern Carpathians, seceding from the Slavs who continued their expansion to the Balkan Peninsula. Dialects of the Slovak language still reflects that the Slavs came from different directions already in the Early Middle Ages, according to a widely accepted scholarly theory. The Czech and Slovak languages share some features with the South Slavic languages, distinguishing them from the other West Slavic languages. According to archaeologist P. M. Barford, these features suggest that the Carpathian Mountains and the Sudetes separated the ancestors of the Slovaks and the Czechs from the Slavs living to the north of those mountains. Especially the dialects of Central Slovakia, which stand out from the continuous chain between the western and eastern dialects, preserved South Slavic features.