By: Drs. Hamidin - BNPP RI Expert Group

The island of Borneo stands as one of Southeast Asia’s most geopolitically significant regions—a shared space where the borders of Indonesia, Malaysia, and Brunei Darussalam intersect, and where history, sovereignty, and natural wealth are deeply intertwined. In the north, Malaysia governs the states of Sabah and Sarawak, while Brunei remains a small yet prosperous sultanate. Between these territories lies a complex web of historical legacies, socio-economic interdependence, and unfinished boundary demarcations that continue to shape the regional landscape of postcolonial Southeast Asia.

Colonial Legacies and the Roots of Dispute

The roots of contemporary border issues trace back to the 19th century, when much of northern Borneo was under the influence of the Brunei Sultanate. Over time, Brunei’s territorial reach diminished through a series of concessions and land grants to European powers. The Brooke dynasty, known as the “White Rajahs,” consolidated their rule in Sarawak, while the British North Borneo Company gained control over what would become Sabah.

These arrangements, often based on ambiguous private charters rather than formal treaties, left behind unclear territorial boundaries. When Malaysia was formed in 1963, colonial administrative lines were adopted as national borders. However, Brunei—achieving full independence in 1984—later sought to revisit some of these arrangements, particularly concerning its borders with Sarawak. The result is a lingering patchwork of historical claims, where colonial-era legacies continue to influence modern sovereignty.

The Limbang Question and Land Demarcation

At the heart of Brunei–Malaysia land boundary issues lies the Limbang district, located between Brunei’s eastern and western territories. Malaysia views Limbang as an integral part of Sarawak, annexed by the British in 1890 following a local uprising. Brunei, however, has historically maintained its claim to the area.

The 2009 Exchange of Letters between both governments was widely interpreted by Malaysia as Brunei’s acknowledgment of its sovereignty over Limbang. Yet, Brunei never made this position explicit. As a result, the issue remains diplomatically delicate—managed through quiet dialogue rather than confrontation, in the spirit of maintaining bilateral goodwill.

Technically, the physical demarcation of the Brunei–Malaysia border remains a challenge, as the terrain cuts through dense forests and river systems. The Joint Land Boundary Technical Committee continues to address these complexities, reflecting how border-making in Borneo involves not only diplomacy but also the logistics of mapping and natural geography.

Maritime Boundaries and Energy Interests

Beyond land, the maritime frontiers surrounding Brunei, Sabah, and Sarawak hold some of Southeast Asia’s richest offshore oil and gas reserves. In the early 2000s, overlapping exploration rights in the South China Sea sparked tensions between Malaysia’s Petronas and Brunei’s Petroleum Authority. The issue was resolved through the 2009 agreement establishing Commercial Arrangement Areas, allowing for joint exploration and development.

Nevertheless, the precise maritime boundaries remain unpublished, leaving certain gray zones open to interpretation. This episode underscores that borders in Borneo are not solely about sovereignty—they are also about strategic resources, national interests, and shared prosperity. Every nautical mile in these waters carries implications for regional stability and economic growth.

Social Fabric and Cross-Border Mobility

The borderlands of Sabah, Sarawak, and Brunei are bound by more than political lines—they are linked by deep cultural and familial ties among the Dayak, Kedayan, and Bruneian Malay communities. Daily life in these regions reflects a fluid social geography where commerce, kinship, and movement transcend borders.

Many Sarawakians commute or migrate to Brunei in search of higher incomes, while Bruneian residents rely on neighboring Malaysian towns for goods and services. This interdependence, while economically beneficial, also challenges the capacity of states to manage informal trade and migration effectively.

For policymakers, the lesson is clear: sustainable border management must balance security with human development. Focusing solely on control risks neglecting the shared livelihoods that have long sustained border communities.

Security Dynamics and Regional Cooperation

Geographically, the borders of Sabah, Sarawak, and Brunei sit at a critical juncture between the Sulu and South China Seas—waters that have seen smuggling, piracy, and cross-border militancy. The 2013 Lahad Datu incident, when armed militants from the Philippines landed in Sabah, prompted Malaysia to strengthen its security apparatus. Indonesia also intensified patrols in North Kalimantan to prevent illegal crossings, while Brunei maintained vigilance through its policy of neutrality and stability.

Recognizing that no nation can tackle these challenges alone, the Trilateral Maritime Patrols (TMP)—involving Indonesia, Malaysia, and the Philippines—were launched in 2017 under ASEAN’s framework. These joint efforts enhance intelligence-sharing and maritime surveillance, demonstrating that regional peace depends on both collaboration and shared prosperity.

Toward Integrated Border Management and Cooperation

In recent years, Southeast Asia’s border narrative has gradually shifted from “lines of separation” to “zones of cooperation.” The Brunei–Indonesia–Malaysia–Philippines East ASEAN Growth Area (BIMP-EAGA) embodies this transformation, fostering connectivity, trade, and infrastructure across the region’s frontier economies.

For Brunei, the initiative diversifies its economy beyond hydrocarbons; for Malaysia, it strengthens the inclusion of Sabah and Sarawak in national development; and for Indonesia, it accelerates growth in North Kalimantan and other peripheral provinces. However, the full realization of this shared vision depends on two crucial elements: clear border demarcation and effective governance. Without these, even the most ambitious cooperation frameworks risk being undermined by uncertainty.

Conclusion

The border issues among Sabah, Sarawak, and Brunei Darussalam illustrate the enduring complexities of nation-building in postcolonial Southeast Asia. Despite historical grievances, the three nations have chosen pragmatism over provocation—managing disputes through diplomacy and focusing on mutual economic gain.

The three nations understand that peace and cooperation yield greater dividends than zero-sum territorial claims. What remains is not merely to draw clearer lines on maps, but to build inclusive border zones—with infrastructure, legal clarity, and prosperity for the people who live along them.

Ultimately, the management of these borders is not a technical exercise alone. It is part of a broader strategy to forge sovereignty with justice and security with humanity in the heart of Borneo.

(Humas BNPP RI)

Footnotes

1. Saunders, Graham. A History of Brunei. Oxford University Press, 1994.

2. Singh, Bilveer. Brunei Darussalam: Security and Defence. ISEAS, 2013.

3. “Exchange of Letters between Brunei Darussalam and Malaysia,” Government of Brunei Darussalam Gazette, 2009.

4. Leong, Ho Khai. “Malaysia-Brunei Territorial Disputes and the 2009 Agreements.” Contemporary Southeast Asia, vol. 32, no. 1, 2010.

5. Chin, James. “Cross-Border Relations in Northern Borneo.” Asian Survey, vol. 49, no. 3, 2009.

6. Banlaoi, Rommel. Maritime Terrorism in Southeast Asia: The Abu Sayyaf Threat. Routledge, 2011.

7. ASEAN Defence Ministers Meeting (ADMM) Joint Declaration, Manila, 2017.