Claim: In 2004, Slovenia joined both NATO and the European Union.

Slovenia -LRB- -LSB- sloʊˈviːniə , _ slə - , _ - njə -RSB- ; Slovenija -LSB- slɔˈʋéːnija -RSB- -RRB- , officially the Republic of Slovenia -LRB- Slovene : , abbr. : RS -RRB- , is a nation state in southern Central Europe , located at the crossroads of main European cultural and trade routes . It is bordered by Italy to the west , Austria to the north , Hungary to the northeast , Croatia to the south and southeast , and the Adriatic Sea to the southwest . It covers 20,273 km2 and has a population of 2.06 million . It is a parliamentary republic and a member of the United Nations , European Union , and NATO . The capital and largest city is Ljubljana .   The territory is mostly mountainous with a mainly continental climate , with the exception of the Slovene Littoral that has a sub-Mediterranean climate and the north-western area that has an Alpine climate . Additionally , the Dinaric Alps and the Pannonian Plain meet on the territory of Slovenia . The country , marked by a significant biological diversity , is one of the most water-rich in Europe , with a dense river network , a rich aquifer system , and significant karst underground watercourses . Over half of the territory is covered by forest . The human settlement of Slovenia is dispersed and uneven .   Slovenia has historically been the crossroads of South Slavic , Germanic , Romance , and Hungarian languages and culture . Although the population is not homogeneous , the majority is Slovene . South Slavic language Slovene is the official language throughout the country . Slovenia is a largely secularized country , but its culture and identity have been significantly influenced by Catholicism as well as Lutheranism . The economy of Slovenia is small , open , and export-oriented and has been strongly influenced by international conditions . It has been severely hurt by the Eurozone crisis , started in the late 2000s . The main economic field is services , followed by industry and construction .   Historically , the current territory of Slovenia was part of many different state formations , including the Roman Empire and the Holy Roman Empire , followed by the Habsburg Monarchy . In October 1918 , the Slovenes exercised self-determination for the first time by co-founding the State of Slovenes , Croats and Serbs . In December 1918 , they merged with the Kingdom of Serbia into the Kingdom of Serbs , Croats and Slovenes -LRB- renamed Kingdom of Yugoslavia in 1929 -RRB- . 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 . Afterward , it was a founding member of the Federal People 's Republic of Yugoslavia , later renamed the Socialist Federal Republic of Yugoslavia , a communist state which was the only country in the Eastern Bloc which was never part of the Warsaw Pact . In June 1991 , after the introduction of multi-party representative democracy , Slovenia split from Yugoslavia and became an independent country . In 2004 , it entered NATO and the European Union ; in 2007 became the first formerly communist country to join the Eurozone ; and in 2010 joined the OECD , a global association of high-income developed countries .