Why Borneo Island Is Divided Between Three Countries?

How Did Borneo End Up Being Split by Three Countries?

Borneo is the third-largest island in the world, covered in lush rainforests, rich biodiversity, and deep cultural roots. But what makes it especially unique is its modern political geography: it’s split between three different countries—Indonesia, Malaysia, and Brunei. How did that happen? The answer, as with many post-colonial puzzles, lies in a mix of empires, treaties, and local politics. Here's the story.

Pre-Colonial Power Struggles: Brunei's Rise and Decline

Before European colonial powers arrived, much of Borneo was under the influence of powerful regional kingdoms. The Sultanate of Brunei rose to prominence in the 15th century, controlling vast areas of northern Borneo and parts of the southern Philippines. However, Brunei’s influence began to wane in the 18th century due to internal conflict, piracy, and pressure from European traders.

As Brunei declined, smaller states emerged, including some unique entities like the Lanfang Republic, a short-lived Chinese mining republic in western Borneo, and the Sarawak Kingdom, which we’ll get to shortly.

The British and Dutch Carve Things Up

In 1824, the Anglo-Dutch Treaty split Southeast Asia into spheres of influence. The British took the northern part of Borneo, and the Dutch claimed the southern portion, which would later become Kalimantan, now part of Indonesia.

By the mid-19th century, northern Borneo saw two unusual developments:

• In Sarawak, an English adventurer named James Brooke helped the Sultan of Brunei quell a rebellion and was rewarded with territory. He became the first of the "White Rajahs", a dynasty that ruled Sarawak as an independent kingdom under British protection.
• Meanwhile, eastern Borneo came under the administration of the British North Borneo Chartered Company, while Brunei shrank further as it ceded more land under pressure.

Eventually, all of these British territories—Sarawak, North Borneo (now Sabah), and Brunei—became British protectorates.

Independence and the Formation of Malaysia

After World War II, the Dutch East Indies declared independence and became modern-day Indonesia, taking with it the Dutch-controlled parts of Borneo (Kalimantan).

On the British side, Malaya gained independence in 1957, and in 1963, it joined with Sarawak, Sabah, and Singapore to form the new nation of Malaysia.

But not everyone joined.

Why Brunei Stayed Out

Brunei was initially invited to join the Malaysian Federation, but it declined. Why?

• Internal unrest: A failed leftist uprising in 1962 (the Brunei Revolt), supported in part by Indonesia, left the Sultan wary.
• Oil wealth: Brunei had discovered massive oil reserves. Joining Malaysia would have meant sharing its revenues with other states.
• Royal ambitions: The Sultan didn’t want to be subordinate in a federation where kingship rotated and where he wouldn’t be the top royal.

So Brunei remained a British protectorate until it achieved full independence in 1984.

The Modern Result: Three Nations, One Island

Today, Borneo is divided as follows:

• Indonesia controls about 73% of the island—its provinces in Borneo are collectively called Kalimantan.
• Malaysia holds the states of Sabah and Sarawak on the northern coast.
• Brunei, a small but wealthy sultanate, remains an independent nation nestled between parts of Sarawak.

Why It Matters

The division of Borneo is more than just a relic of colonialism. It still influences regional politics, resource management, and identity. For example:

• Sabah and Sarawak have ongoing political debates in Malaysia about autonomy and revenue-sharing.
• Brunei continues to maintain its wealth and monarchy while being surrounded by larger neighbors.
• Indonesia is even building its new capital, Nusantara, in East Kalimantan—an effort to develop its part of the island further.

Echoes of Empire

Borneo’s split is a living reminder of how colonial borders, local kingdoms, and global politics intersect. It's a story of shifting power, oil politics, forgotten republics, and British adventurers turned kings. In many ways, the island’s modern-day borders are not the result of one singular decision, but a century-long domino effect of empires rising, falling, and bargaining for influence—each leaving its mark on this magnificent island.