Following the breakup of Yugoslavia in 1991, Slovenia and Croatia became independent countries. As the border between the countries had not been determined in detail prior to independence, several parts of the border were disputed, both on land and at the sea, namely in the Gulf of Piran.
According to the Croatian Bureau of Statistics, the two countries share about of border. According to the Statistical Office of the Republic of Slovenia, the border spans . The border mostly runs along a southwest-northeast axis.
The countries have attempted to resolve the dispute, most notably with the Drnovšek–Račan agreement in 2001 that was ratified by Slovenia but not by Croatia. Because of the disputed border, Slovenia blocked Croatia's EU accession talks until the agreement was reached by both countries and the EU to settle the dispute by a binding arbitration.
On 29 June 2017, the Permanent Court of Arbitration issued a binding ruling on the border, ruling on the disputed parts of land border, drawing the border in the Gulf of Piran, and ruling that Slovenia should have direct access to international waters in the north Adriatic Sea using a corridor crossing Croatian waters. It also ruled on several other disputed border areas. The ruling was hailed by Slovenia but Croatia said it would not implement it. Croatia stated that they withdrew from the process in 2015, citing the discovered talks between the Slovenian government representative and the member of the arbitration court as a breach of the arbitration rules. Slovenia implemented the ruling on 29 December 2017 with continued opposition from Croatia.
Origins of Gulf of Piran issues
Following World War II, the area from north of Trieste to the Mirna River in the south was part of the Free Territory of Trieste. In 1954, the Territory was dissolved; the area was provisionally divided between Italy and Yugoslavia, and the division made final by the Treaty of Osimo in 1975.
In the first draft delimitation proposal following both countries' 1991 declarations of independence, Slovenia proposed establishing the border in the Gulf of Piran's center. However, Slovenia changed the draft the following year (declaring its sovereignty over the entire Gulf on 5 June 1992). Since then Slovenia has continued to insist on this position.
The name "Bay of Savudrija" () was originally used for only part of the bay. In 2000 it came into use for the whole bay by local Croatian fishermen and was quickly adopted (first by Croatian journalists, then local authorities, and finally at the state level), leading to its appearance in official maps. Such actions were contrary to established practices with long-standing geographical names, and are seen by Slovene authorities as an attempt to imply historical connections with the bay. Another name, "Bay of Dragonja" (), was introduced in Croatia but failed to gain widespread use.
Sea dispute
Croatia claims that the boundary should be an equal distance from each shore. The claim is based on the first sentence of Article 15 of the United Nations Convention on the Law of the Sea:
Slovenian claims are based on the same article. However, it favours the second sentence, which stipulates that historical claims or other unusual circumstances supersede the equidistance rule. The Law of the Sea also states that international waters begin from the country's shore – while the nearest international waters are away from Slovenia's shore.
The Convention states that a coastal state has an exclusive right to manage all natural resources in a band up to from its shore (an 'exclusive economic zone').
When Slovenia notified the UN Secretariat in 1995 of its succession to Yugoslavia's ratification of the Convention (continuing the agreement), it included a note saying that this system of exclusive economic zones has become part of international law and asserted its rights as a geographically disadvantaged state. The convention makes it clear that any decision to declare an exclusive economic zone should be made in co-operation with all interested parties; Croatian sources claim that Slovenia's self-description as a geographically disadvantaged state amounts to an admission that it is a country without access to international waters.
Slovenia also claims the right to access international waters; Slovenia bases this claim on the country's free access to international waters while part of Yugoslavia. Due to the statements of Croatian negotiators, Slovenian politicians have also presented the concern that without a territorial connection to international waters, Croatia could limit "harmless passage" to its ports (contrary to international agreements and practice); this would complicate Slovenia's sovereignty at sea and could cause economic damage. Because of these concerns, Slovenia has invoked the principle of equity for unfortunate geographic conditions.
According to Slovenia, Savudrija was associated with Piran, which for centuries had an Italian majority until post-World War II, and Slovenian police controlled the entire gulf between 1954 and 1991. If this claim were to prevail, Slovenia argues it could claim sovereignty over part of the bay area on the Croatian side of the median line. Croatia disputes Slovenia's claims of historical control over the bay.
The Croatian side asserts that the corridor in the Croatian waters would be useless for traffic, since traffic regulations in the Gulf of Trieste allow only incoming traffic on the Croatian side of the border, while outgoing traffic must go through Italian waters. The Slovenian response is that Slovenia's access to international waters is not an exclusively practical or commercial issue; it is rather the logical consequence of that Slovenia is said to be an internationally recognized maritime country with granted access to international seas. The latter assertion has been repeatedly disputed by the Croatian side.
Croatia wants to solve this dispute only by certain articles of international law, while the Slovenian side insists on consideration of the principle "ex aequo et bono". The disputed points between the countries include whether or not the legal principle "ex aequo et bono" is a part of international law. Article 38(2) of the Statute of the International Court of Justice provides that the court may decide cases ex aequo et bono only if the parties agree. In 1984, the ICJ decided a case between the U.S. and Canada using "equitable criteria".
According to the Wikileaks cables published in 2011, which contain assessments by American diplomats, the maritime border dispute was influenced by Slovenia considering itself a maritime nation and Croatia feeling inferior to its neighbours.
Land dispute along the Dragonja river
Along with the maritime dispute, the two countries also have a land border dispute in the Gulf area along the Dragonja River. As in other disputed border areas, the dispute stems from differing demarcation principles: while the border between two republics was often drawn based on (sometimes loose) political agreements or along natural landforms, cadastral records from villages along the border continued to refer to the land which ended up controlled by the other republic. In the delta of Dragonja, Slovenia claims that the border is south of the river (thus including all the land that is registered in the cadastral municipality of Sečovlje), while Croatia claims that the border is on the river itself (St. Odoric's canal). The Croatian side rejects Slovenian arguments for cadastral borders on just this part of the mutual border (where such are in favour of Slovenia), saying that if the cadastral principle was consistently implemented, Slovenia would lose much more territory elsewhere than it could receive in the Gulf of Piran.
Another source of conflict in this area has been the border crossing at Plovanija, due to a checkpoint unilaterally established by Croatia on territory that has been claimed by both sides. Despite stating that the border crossing checkpoint is only a temporary solution, Croatia has included this checkpoint as indisputable in its international documents. Consequently, the territories with a Slovenian population south of that border checkpoint are considered to be under Croatian occupation by a number of Slovenian politicians and legal experts.
Both countries claim to have exercised since 1954 the most administrative jurisdiction over the contested area on the left bank of the river. The strip's inhabitants were granted Slovenian citizenship in 1991 and the Slovenian judiciary considers the area an integral part of Slovenia.
Among the Slovenian citizens residing in the area on the left bank of the Dragonja river is Joško Joras, whose refusal to recognize any Croatian jurisdiction after the two countries' independence has led since the early 1990s to a number of conflicts between Slovenia and Croatia. Joras claims he is on Slovenian territory occupied by Croatia; this has garnered much local public, but not much international, attention.
According to some Croatian experts, the border between the countries should be a few miles north from the current Dragonja river course, on what they regard as the original river course. The current river flow is actually a man-made canal, known as the Canal of St. Odoric. They point out a 1944 meeting organized by the Partisan Scientific Institute, led by the Slovenian historian Fran Zwitter, at which Slovenian and Croatian officials agreed on the Dragonja river as the border between the Socialist Republics of Croatia and Slovenia. However, neither the Slovenian nor the Croatian parliament ever ratified the agreement, nor was it ever internationally recognized. Moreover, according to some Slovenian legal experts such as Pavel Zupančič, the last internationally recognized border between the two countries was on the river Mirna (south of the Dragonja). However, the proposed Dragonja border has also been referenced multiple times and even partially implemented. The Croatian argument is, accordingly, based exclusively on the Dragonja border proposal which Slovenia has never officially recognized. According to the Croatian view, the current main flow of the Dragonja (the Canal of St. Odoric) was man made; according to Dr. Ekl, while international law allows changes of river-defined borders when rivers are changed by nature, it does not allow man-made river changes to alter borders. However, this is not the Croatian government's official position.