What makes Southeast Asia a region

The one without a coast

Laos is bordered by China, Myanmar, Thailand, Cambodia and Vietnam, and by no sea. Its lowest recorded point is the Mekong at one metre and its highest is Phou Bia at 2,819 metres, so the country lies either in the river's basin or on the ranges above it. The Mekong touches five of the members filed here. The treaty that governs the lower river covers four: Cambodia, Laos, Thailand and Vietnam signed the Agreement on the Cooperation for the Sustainable Development of the Mekong River Basin on 5 April 1995 and sit on the commission it created, while Myanmar and China deal with it as dialogue partners from outside. The river and the institution built on it are not the same shape.

The roster and the group became the same list

Five states signed the Bangkok Declaration on 8 August 1967: Indonesia, Malaysia, the Philippines, Singapore and Thailand. Brunei acceded on 8 January 1984, a week after independence; Vietnam on 28 July 1995; Laos and Myanmar together on 23 July 1997; Cambodia on 30 April 1999. Timor-Leste was admitted on 26 October 2025, and from that date the membership of the Association of Southeast Asian Nations and the roster filed under this region hold the same 11 countries. For the fifty-eight years before it they did not.

Which way the traffic runs

Brunei, Indonesia, Malaysia, Singapore, Thailand and Timor-Leste keep to the left. Cambodia, Laos, Myanmar, the Philippines and Vietnam keep to the right, and the line between the two groups follows the administering power of the early twentieth century rather than the map. Myanmar is the exception on its own side: traffic moved from the left to the right by decree in 1970, the vehicles were not changed with it, and most cars on the road there still have the steering wheel on the offside.

The clocks, and what is in the till

Myanmar holds a single offset of UTC+06:30, the one half hour in the region. Indonesia holds three, from UTC+07:00 at Jakarta to UTC+09:00 at Jayapura, and records a second capital at Nusantara beside it; Malaysia likewise records Putrajaya beside Kuala Lumpur. Ten members issue money of their own. Timor-Leste does not: the United States dollar has been legal tender there since 2000, under a regulation of the United Nations transitional administration, with centavo coins struck locally to go beside it. Two of the ten circulate interchangeably. Brunei and Singapore have taken each other's notes and coins as customary tender since the agreement of 12 June 1967, to which Malaysia was also a party until 1973.

Where the edges are argued

The M49 standard of the UN Statistics Division files exactly this list under South-eastern Asia, and states that its groupings carry no political meaning. Two edges are argued anyway. Timor-Leste is grouped here on the strength of the island it shares with Indonesia, and read into Melanesia elsewhere on the strength of its languages and its membership of the Melanesian Spearhead Group. Indonesia reaches east across the Sahul shelf onto New Guinea, ground that belongs geologically to Australia rather than to Asia. The catalogue records both readings and settles neither.