While islands are often thought of as unified, sovereign territories surrounded by water, a surprising number of them are split between two different countries. These divided islands tell stories of colonialism, conflict, negotiation, and coexistence.
From the mountains of Papua to the dense jungles of Borneo, and from the green hills of Ireland to the frigid lands of Tierra del Fuego, borders have been drawn right through island landscapes.
Ireland (United Kingdom and Republic of Ireland)
Ireland is one of the most well-known politically divided islands. The island is split between Northern Ireland, which is part of the United Kingdom, and the Republic of Ireland, a sovereign nation.
The border between them is a product of the Government of Ireland Act of 1920 and subsequent Anglo-Irish Treaty of 1921, which ended the Irish War of Independence and established Northern Ireland as a distinct entity within the UK.
While the border was historically a flashpoint during "The Troubles", a period of sectarian conflict from the late 1960s to the 1990s, the Good Friday Agreement of 1998 largely ended the violence and brought relative peace.
The border is now soft and often invisible, although it has become a sensitive issue again in the context of Brexit. Despite political divisions, cultural, linguistic, and familial ties often stretch across both sides of the island.
Borneo (Indonesia, Malaysia and Brunei)
Borneo is the third-largest island in the world and uniquely divided among three countries: Indonesia, Malaysia, and the small nation of Brunei. The Indonesian portion, known as Kalimantan, occupies about 73% of the island.
Malaysia controls the northern parts, Sabah and Sarawak, while Brunei is a tiny sultanate wedged between Malaysian territory on the northern coast.
The divisions on Borneo stem from colonial legacies, with Indonesia inheriting Dutch control and Malaysia and Brunei tracing their administrative roots to British rule.
While the island has seen periods of tension, especially over environmental and resource issues, there are no active border conflicts today. However, differing policies on logging, conservation, and indigenous rights continue to create sharp contrasts between the regions.
Papua (Indonesia and Papua New Guinea)
The island of New Guinea, of which Papua refers to the western half, is divided between Indonesia and Papua New Guinea.
Indonesia controls the western part of the island, encompassing the provinces of Papua and West Papua, while Papua New Guinea occupies the eastern side as an independent country.
This division is one of the more politically and culturally tense island splits. While Papua New Guinea gained independence from Australia in 1975, the Indonesian side was annexed in the 1960s through a controversial process that followed Dutch withdrawal.
Many indigenous Papuans continue to call for independence or greater autonomy, and Indonesia’s presence in the region has been marked by allegations of human rights abuses and militarization.
Hispaniola (Haiti and the Dominican Republic)
The island of Hispaniola, located in the Caribbean, is shared by Haiti and the Dominican Republic.
Haiti occupies the western third of the island, while the Dominican Republic controls the eastern two-thirds. The division dates back to colonial times when Spain and France controlled different parts of the island.
Today, the two countries share a tense relationship, despite their geographical proximity. The border is marked by stark contrasts in economic development, language, and public health.
Haiti remains one of the poorest countries in the Western Hemisphere, while the Dominican Republic enjoys relatively higher levels of prosperity and tourism.
Migration from Haiti into the Dominican Republic has caused political friction, leading to periodic crackdowns and disputes over citizenship and labor rights.
Sebatik (Indonesia and Malaysia)
Sebatik Island is located off the eastern coast of Borneo and is split between Indonesia and Malaysia.
The division is nearly straight and cuts through the island from north to south, with the northern section belonging to Malaysia's Sabah state and the southern portion part of Indonesia’s North Kalimantan province.
The split is rooted in British and Dutch colonial treaties, and although it’s a relatively quiet border today, it has seen disputes, especially regarding maritime claims off the coast.
Life on Sebatik reflects the broader differences between Malaysia and Indonesia in infrastructure, public services, and governance. Despite these differences, cross-border family ties and cultural exchanges persist.
Timor (Indonesia and Timor-Leste)
Timor Island is split between Indonesia, which controls the western half, and Timor-Leste (East Timor), which gained independence in 2002 after a long and violent struggle.
The eastern half had been a Portuguese colony until 1975, after which Indonesia annexed it, sparking decades of conflict. The people of East Timor overwhelmingly voted for independence in a 1999 referendum.
The western half remains under Indonesian administration as part of East Nusa Tenggara province. The two sides of the island have distinct colonial legacies, languages, and political systems, although cultural and ethnic overlap remains strong.
The border between them is mostly peaceful today, though some disputes persist, particularly regarding land use and demarcation in rural areas.
Isla Grande de Tierra del Fuego (Argentina and Chile)
At the southern tip of South America lies Isla Grande de Tierra del Fuego, shared by Argentina and Chile. The island is divided by the 1881 Boundary Treaty, which split the land roughly in half, with the eastern portion going to Argentina and the western part to Chile.
Despite a history of tension between the two countries, including near-conflict over territorial claims in the Beagle Channel during the 1970s, the island itself has been relatively calm.
Today, the Argentine city of Ushuaia is a hub for Antarctic tourism, while Chile maintains the smaller town of Porvenir. The landscape is rugged and sparsely populated, with shared ecological concerns increasingly drawing the two nations into environmental cooperation.
