Several European territories have unilaterally declared independence since the end of World War II, mainly because of the collapse of the Soviet Union and Yugoslavia.
But none has officially broken away from the European Union, created in 1993, even though movements demanding more independence exist in various countries.
Catalonia's declaration of independence is a first for the European Union.
The collapse of the Soviet Union led to the biggest wave of independence movements in Europe since 1945.
In March 1990, Lithuania became the first Soviet republic to declare independence. Soviet troops intervened in January 1991, but withdrew after a confrontation in which 13 people were killed.
In June, Russia proclaimed its sovereignty under Boris Yeltsin. Nine Soviet republics went on to declare their independence in August and September.
In December the same year, Russian, Ukrainian and Belarussian leaders signed a treaty ending the Soviet Union and formalising the creation of 15 countries, including the three Baltic States (Estonia, Latvia and Lithuania) which joined the EU in 2004.
Separatist tensions in the post-Soviet region still persist today.
Transdniestr, a region of Moldova mainly inhabited by Russian speakers, proclaimed its independence and took up arms in 1992. But it is recognised by no other state.
Abkhazia and South Ossetia, two separatist regions in Georgia, were at the root of the Russia-Georgia conflict in August 2008. The conflict ended with Moscow's recognition of the two regions' independence but only Nicaragua, Venezuela and Nauru have done the same.
In Ukraine the two separatist self-styled "republics" of Lugansk and Donetsk declared their independence in 2014, after referendums. Largely dependent on Russia, they are not recognised by the international community.
The first of six republics to leave the socialist federation of Yugoslavia were Slovenia and Croatia which declared their independence in June 1991.
In Slovenia the process was largely peaceful: the Yugoslav army withdrew after 10 days of skirmishes. The country became, in 2004, the first former Yugoslav state to join the EU.
In the case of Croatia, war broke out as the Serb minority, backed by the then Yugoslav capital Belgrade, refused the independence. The conflict, which caused 20,000 deaths, ended in 1995. Croatia entered the EU in 2013.
Macedonia declared independence peacefully in 1991 after 95 percent voted "yes" in a referendum.
In Bosnia Herzegovina the proclamation of independence in 1992, after a referendum boycotted by its Serb minority, sparked a three-and-a-half-year long war between Muslims, Serbs and Croats.
Nearly 100,000 died and 2.2 million became refugees. Belgrade only recognised Bosnia in November 1995.
The small country of Montenegro declared independence from Serbia in 2006.
The last country to be born from the ruins of the former Yugoslavia is Kosovo which declared independence in 2008 after a first referendum in favour of autonomy in 1991, followed by a guerrilla movement against Serb forces.
Kosovo is recognised by more than 100 countries, but not by Belgrade. It does not have a seat at the UN.
In 1974 Greek Cypriot nationalists, backed by Athens, launched a coup aimed at joining the former British colony to Greece.
The coup broke down after a few days but not before Turkish troops invaded the north of the Mediterranean island to protect the Turkish Cypriot minority.
In November 1983 the breakaway Turkish Republic of Northern Cyprus was declared, covering 38 percent of the territory and where Turkish troops are still deployed. Only Ankara recognises the entity.
In 2004 the divided island joined the EU but its laws only apply to the non-Turkish-held southern part of the republic.