Analysis of information sources in references of the Wikipedia article "Slovenes" in English language version.
[...] the former inhabitants of the lands of modern Slovenia [...] were overwhelmed by the Slovenes during the migration of nations after 500 AD. In the 6th century AD, west Slavic tribes who had come through Moravia into the eastern Alps, began to dominate the entire area along the Danube between Vienna and Linz and from the High Tauern below Salzburg to Trieste bay the Adriatic. Around 200,000 people lived on this territory, three times bigger than contemporary Slovenia.
The Slavs settled the present-day Slovene territory in the period between 568, when the Lombards moved from Pannonia to Italy, and the last decade of the 6th century, when the Slavs were already clashing with the Bavarians in the Upper Drava Valley and penetrating into Italy across Istria or the Karst.