In December 1918, they merged with the Kingdom of Serbia into the Kingdom of Serbs, Croats and Slovenes (renamed Kingdom of Yugoslavia in 1929).
During World War II, Slovenia was occupied and annexed by Germany, Italy, and Hungary, with a tiny area transferred to the Independent State of Croatia, a Nazi puppet state.
Consequently, the Frankish feudal system reached the Slovene territory.
After the victory of Emperor Otto I over the Magyars in 955, Slovene territory was divided into a number of border regions of the Holy Roman Empire.
This article is about the country bordering the Adriatic Sea.
For the landlocked country to its northeast, see Slovakia.
A part of the inner state was protected with a defensive line of towers and walls called Claustra Alpium Iuliarum.
The area that is present-day Slovenia was in Roman times shared between Venetia et Histria (region X of Roman Italia in the classification of Augustus) and the provinces Pannonia and Noricum.
In 2002, remains of pile dwellings over 4,500 years old were discovered in the Ljubljana Marshes, now protected as a UNESCO World Heritage Site, along with the Ljubljana Marshes Wooden Wheel, the oldest wooden wheel in the world.
In the transition period between the Bronze age to the Iron age, the Urnfield culture flourished.
After its disintegration following Samo's death in 658 or 659, the ancestors of the Slovenes located in present-day Carinthia formed the independent duchy of Carantania.
The Carantanians, one of the ancestral groups of the modern Slovenes, particularly the Carinthian Slovenes, were the first Slavic people to accept Christianity.