On 8 April, Malaysia and Singapore suspended the implementation of overlapping port limit claims in the Johor Strait, in a move to de-escalate a maritime border dispute which for the past six months has threatened to damage ties between the two Southeast Asian neighbors. The row has been indicative of revived tensions in bilateral relations since veteran Malaysian Prime Minister Mahathir Mohamad returned to power in Kuala Lumpur after a shock election victory a year ago. Disputes have also arisen over the control of airspace, a long-standing water supply agreement, and a high-speed railway project.

While tensions in the maritime realm have eased and both sides have agreed to enter into a dialogue process to delineate the sea border, the dispute itself remains unresolved and could flare up again in the future. Another round of hostility between Malaysia and Singapore would cause great concern to major trading nations, reliant on the free movement of shipping in the vital sea lanes upon which the two countries sit and exercise control. What caused the sudden flare up of the simmering dispute in late 2018? And with tensions receding across the Johor Strait, what are the prospects for resolution?

Revival of a decades-old maritime dispute

The border dispute has its origins in a 1979 map published by Malaysia, outlining its claimed territorial waters. Singapore lodged a strong diplomatic protest at the time, arguing the boundary lines intruded into its port limits. Despite these complaints, in 1987 Malaysia marked the boundary of its own port at Johor Bahru in accordance with the lines claimed on the disputed 1979 map. The two countries reached an agreement in the mid-1990s on the delimitation of sea boundaries and Singapore has since exercised jurisdiction over the entirety of its claimed territorial waters without protest from Malaysia.

The issue lay dormant for more than 20 years, during which time both nations enjoyed relatively stable bilateral ties. The situation changed abruptly in October 2018, when the Malaysian government published a document extending its port limit beyond the territorial sea claim made in the 1979 map. Singaporean leaders reacted furiously. Transport Minister Khaw Boon Wan accused Kuala Lumpur of ‘seeking to alter unilaterally the long-standing status-quo in the area, without any prior consultation,’ adding that ‘this is a blatant provocation and a serious violation of our sovereignty and international law.’