Indonesia faces the challenge of settling maritime boundaries with 10 neighboring states, including India, Malaysia, and Australia. This task is further complicated by its efforts to extend its Extended Continental Shelf (ECS) beyond 200 nautical miles from the baselines from which the breadth of the territorial sea is measured, which would require new negotiations with the Federated States of Micronesia (FSM). Despite these potential difficulties, Indonesia remains committed to expanding its maritime entitlements through legal means, following the precedent set by the 1957 Djuanda Declaration, which unilaterally asserted that Indonesia’s land and surrounding seas formed a unified archipelagic territory, an idea later enshrined in international law through its recognition in the 1982 U.N. Convention on the Law of the Sea (UNCLOS).
Under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS), coastal states can claim an ECS based on scientific evidence pertaining to issues, including seabed morphology and sediment thickness. Indonesia is currently pursuing this process through submissions to the U.N. Commission on the Limits of the Continental Shelf (CLCS). Between 2008 and 2022, it made four submissions to extend its sovereign rights over the continental shelf, underscoring the proactive nature of the border diplomacy that the Foreign Ministry has led since the 1950s, which intensified with the democratization of foreign policy at the turn of the century.
Once approved, these submissions will significantly expand Indonesia’s recognized seabed area, granting the country access to potential natural resources and enhancing its strategic influence. However, this expansion may also create new maritime overlaps, such as with the FSM north of Papua, requiring further negotiations.
Was there a specific strategic logic behind these four submissions? If so, how should we conceptualize Indonesia’s border diplomacy strategy?
We argue that analyzing Indonesia’s ECS submissions reveals the nature of its border diplomacy strategy and demonstrates its willingness to engage in maritime disputes – provided its claims remain anchored within UNCLOS.
The Djuanda Declaration and Indonesia’s Border Diplomacy Strategy
Unlike China, which selectively invokes UNCLOS provisions to justify its maritime claims, Indonesia treats UNCLOS as a comprehensive framework. Indonesia’s success in securing international recognition of the 1957 Djuanda Declaration, through the incorporation of archipelagic principles into UNCLOS, has made the Convention intertwined with its national identity. As a result, Jakarta, and particularly the Foreign Ministry, has positioned itself as a regional guardian of UNCLOS, advocating for its consistent and comprehensive application.
At the same time, Indonesia views UNCLOS as a dynamic legal framework, shaped by state practice, and actively seeks to influence its evolution to maximize its strategic interests, including access to underwater resources. Adopted in 1982, UNCLOS came into force in 1994, replacing the limited 1958 Geneva Conventions. Its implementation has evolved through state practice, court rulings, and shifting geopolitical realities, even though its core framework remains intact.
Indonesia’s approach to border diplomacy has sought to leverage the evolving nature of UNCLOS to shape legal precedents and influence maritime boundary interpretations. This strategy reflects the legacy of the Djuanda Declaration. Prior to the Declaration, Indonesia’s territorial sea extended only three nautical miles, leaving vast waters between its islands as high seas. In response, Prime Minister Djuanda Kartawidjaja, Minister for Veterans’ Affairs Chairul Saleh, and legal scholar Mochtar Kusumaatmadja declared these waters part of Indonesia’s territory. This claim significantly expanded Indonesia’s maritime reach. Initially a unilateral claim, the 1957 Djuanda Declaration—asserting Indonesia as a single unified archipelagic entity—was later enshrined in the 1982 UNCLOS under the “archipelagic state” provisions, notably Article 47, which granted Indonesia the right to draw straight baselines around its outermost islands and exercise full sovereignty over the enclosed waters, airspace, seabed, and subsoil.
Indonesia’s border diplomacy strategy builds on this legacy in two primary ways.
First, Indonesia operates on the principle that no victory is too small, and that each success strengthens its position for future claims. It seeks to shape UNCLOS’ interpretation by promoting legal arguments and establishing consistent state practices in order to influence the framework in its favor. For example, Indonesia’s consistent rejection since 1996 of Malaysia’s single boundary stance and its 2023 delimitation treaty with Vietnam, which reinforced the dual boundaries concept (in which the EEZ and Continental Shelf are separated), illustrate this approach. Indonesia uses successes with one neighbor to support its preferred interpretation, even when it conflicts with others, while maintaining peaceful relations and good diplomatic ties with all.
Second, Indonesia adopts expansive legal interpretations to extend its maritime claims, particularly regarding territorial and maritime boundaries, while adhering to the UNCLOS framework. The map of Indonesia published by the Coordinating Ministry for Maritime Affairs in 2017 reflects this maximalist approach, featuring extensive territorial claims, such as renaming parts of the South China Sea the “North Natuna Sea,” and suggesting a “natural prolongation” of its continental shelf beyond the 200-nautical-mile limit.
These two approaches in Indonesia’s border diplomacy strategy are further unpacked below in terms of Jakarta’s quest to extend its continental shelf beyond 200 nautical miles.
Indonesia’s Strategic Use of Extended Continental Shelf Submissions
The illustration below demonstrates Indonesia’s strategic use of legal instruments – such as continental shelf submissions, unilateral declarations, and strategic legal claims – to extend its sovereign rights under UNCLOS. By relying on Article 76 of the convention, Indonesia ensures that its continental shelf extension adheres to recognized international procedures while expanding its maritime entitlements.
Under Article 76, coastal states are entitled to sovereign rights over the continental shelf beyond their 200-nautical-mile EEZs if they can provide geological and geomorphological evidence that the seabed is a natural prolongation of their land territory. This process enables states to access valuable resources, clarify maritime boundaries, and reduce disputes. States must submit an ECS to the CLCS within 10 years of ratifying UNCLOS, though extensions have been granted. The CLCS reviews submissions to determine their validity based on its scientific and technical guidelines elaborated in Article 76.
On June 16, 2008, Indonesia made its first ECS submission to the CLCS for an area northwest of Sumatra Island. The submission sought to extend Indonesia’s sovereign rights over 4,209 square kilometers of seabed, an area roughly six times the size of Singapore. The CLCS recommended this claim, legally recognizing the seabed as part of Indonesia’s continental shelf.
This success reinforced a key precedent by not only confirming Indonesia’s entitlement beyond the 200-nautical-mile limit but also upholding the UNCLOS principle that coastal states can extend seabed rights based on geological and geomorphological evidence. Indonesia specifically cited tectonic continuity (e.g., the Sunda Shelf and Sunda Arc subduction zone) and sediment thickness to justify its claims under Article 76 of UNCLOS. By securing international recognition through UNCLOS procedures, Indonesia emphasized that legal compliance, rather than military assertion, is the legitimate means of securing maritime entitlements.
More importantly, this success established a legal benchmark for future submissions. Winning the extension in 2008 provided Indonesia with a legal and procedural foundation for further ECS submissions (illustrated above in yellow) in 2019, 2020, and 2022, which involved extensions north of Papua, southwest of Sumatra, and to the south of Java and Nusa Tenggara, respectively.
These later claims follow the same legal reasoning, further strengthening Indonesia’s maritime position under UNCLOS. The 2022 submission, in particular, invoked tectonic continuity – specifically, the collision between the Australian and Banda Sea Plates. Together, these claims cover 653,677.6 square kilometers – an area slightly larger than the U.S. state of Texas – and are currently under CLCS review. If recommended, they would significantly expand Indonesia’s continental shelf, reinforcing its legal maritime entitlements.
Despite following the same legal reasoning, Indonesia adapted each submission to its specific case. For example, while the 2008 submission used the Gardiner Line Formula – based on sediment thickness – the 2019, 2020, and 2022 submissions applied the Hedberg Line Formula, which extends the continental shelf 60 nautical miles from the foot of the continental slope.
Indeed, each submission serves distinct strategic interests. The 2019 submission extends Indonesia’s rights into the Pacific Ocean, overlapping with the FSM’s submission and potentially requiring future boundary negotiations, provided that both submissions are recommended by the CLCS. If this is the case, Indonesia could strengthen its presence in the Pacific while securing seabed resources in a geopolitically sensitive region.
The 2020 submission reinforces Indonesia’s access in the Indian Ocean, a region with significant hydrocarbon potential, bolstering energy security and economic interests. The 2022 submission, the largest claim, covers a vast southern seabed area known for deep-sea geological formations, positioning Indonesia for long-term maritime resource exploration.
By securing its initial extension in 2008, Indonesia not only expanded its reach but also cemented its strategic and economic interests within a firm legal framework, aligning with the two key approaches of its border diplomacy strategy.