While recent global attention has focused on the Strait of Hormuz, which Iran has effectively held closed since late February in a move that has disrupted world energy supplies, a quieter but also important development has been taking shape in south-east Asia.

On April 14, the US and Indonesia announced a "major defense cooperation partnership", strengthening their military ties. According to reports, the US is also seeking to gain wider access to Indonesian airspace. Several media outlets say Indonesia's president, Prabowo Subianto, has approved the proposal.

These developments matter because Indonesia's vast archipelago sits astride some of the most critical sea routes in the world. These include the Strait of Malacca, an important chokepoint for global shipping and trade. The region surrounding Malacca has seen growing military attention from outside powers in recent years.

Both the US and China have been steadily expanding their military presence around the strait and its approaches. The US has largely done so through base access and naval deployments, and China through its port network and naval buildup.

The Andaman and Nicobar Islands, located near the strait's western approaches, also provide India with a strategic presence in the region.

South-east Asia is becoming more explicitly tied into great-power competition, with the new US-Indonesia defense partnership adding the latest layer. Should this competition intensify – whether through a crisis in Taiwan, a spillover from Hormuz or a shift in alliances – the Strait of Malacca would be at the center of it.

The Strait is the shortest sea route connecting the Indian Ocean to the South China Sea and Pacific Ocean, making it the default corridor for trade between East Asia and the West. It stretches roughly 900 kilometers from the Malay Peninsula to the Indonesian island of Sumatra. At its narrowest point, the Phillips Channel near Singapore, it is barely 2.8 kilometers wide.

Almost 24% of global seaborne trade by volume flows through the strait. It carries 45% of the world's seaborne oil, over 25% of all cars traded internationally and 23% of dry bulk cargo including key agricultural commodities like grains and soybeans.

A large portion of European imports of electronics, consumer products like footwear and toys, machinery and industrial goods pass through the strait in sea containers as well.

The strait is also home to some of the world's most critical port infrastructure. Singapore, located at the strait's southern entrance, is the second-busiest container port and the busiest container transshipment hub on the planet.