Maritime security and regional interdependence in the tri-border area: Malaysia’s experience in the Sulu–Celebes sea

The Tri-Border Area (TBA) of the Sulu–Celebes Sea, shared by Malaysia, Indonesia and the Philippines, remains a critical zone for regional security. Persistent non-traditional threats including kidnapping-for-ransom, smuggling, irregular migration, terrorism and other cross-border crimes continue to undermine stability, particularly along the east coast of Sabah. This paper uses Malaysia’s experience as a case study to analyse security challenges in the TBA, arguing that these threats are interconnected and deeply rooted in the region’s geographical and socio-political context. Drawing on Regional Security Complex Theory (RSCT), the study conceptualises the TBA as a regional security subcomplex in which threats operate primarily at the regional rather than global level. By situating Malaysia’s operational and policy challenges within this framework, the paper demonstrates how domestic insecurities are embedded in broader regional dynamics involving the Philippines and Indonesia. The paper contributes to both Malaysian security discourse and regional security studies by extending RSCT to a peripheral maritime frontier dominated by non-traditional threats, emphasising the need for coordinated regional responses rather than unilateral measures.