list of countries that only border one other country

This is a list of countries that only have a land border with one other country. The list includes dependent territories and some de facto independent disputed or occupied areas and unrecognised countries. Nations that only share a land border with one other country often have concerns about domination by the other state if it is larger. These can be fears of an outright take-over as has happened historically to such states as Timor Leste, which was part of Indonesia until very recently, and Ireland, which was part of the United Kingdom until 1921. Today concerns are often about economic domination such as between Canada and the United States or between Denmark and Germany. Because much trade goes over land these countries are often heavily reliant on their single neighbour.

Landlocked and completely surrounded (Enclaves)

Peninsulas/isthmuses

Denmark - with Schleswig-Holstein, Germany - (the island of Zealand is connected to Sweden by the resund Bridge)
Gibraltar - with Spain
Qatar - with Saudi Arabia
South Korea - with North Korea (across the Demilitarized Zone)
Singapore is connected to Johore, Malaysia through a causeway and a bridge.

Partly surrounded, with sea access

Sharing a long border

Canada - with the United States (partly along 49th parallel and with Alaska)

Sharing an island

Brunei - Borneo, with Sarawak, Malaysia
Dominican Republic - Hispaniola, with Haiti
Haiti - Hispaniola, with the Dominican Republic
Republic of Ireland - with Northern Ireland, United Kingdom
The Netherlands Antilles - with Guadeloupe, an overseas department of France, on Sint Maarten/Saint-Martin
Papua New Guinea - with Papua, Indonesia
Timor Leste - Timor, with West Timor, Indonesia
United Kingdom - Northern Ireland, with the Republic of Ireland (the Channel Tunnel connects England with France)

The United States has an enclave under lease from Cuba, Guantanamo Bay, which consists of a military base.

Former countries

Biafra: initally bordered Cameroon and Nigeria after its declaration of independence in early 1967, but territorial gains by Nigeria during the Biafra War left it only bordering Nigeria by later that year, and loss of coastal territories later left it an enclave. See this map
Crimea, declared independence from Ukraine in 1992 but soon settled for being an autonomous republic within Ukraine
Dominion of Newfoundland, with Canada, now the province of Newfoundland and Labrador of Canada
Ciskei, one of the South African "independent" homelands, reincorporated on April 27, 1994

Anomalies

Dhekelia (part of the sovereign base areas of Akrotiri and Dhekelia) is on UN buffer zone between Cyprus and the Turkish Republic of Northern Cyprus, bordering both of them. Technically Cyprus and the Turkish Republic of Northern Cyprus do not border each other immediately, as separated by the UN buffer zone.