1. Canada – United States border: (8,893 km)
Canada, the world’s second largest country in terms of geographic area, and the United States (fourth largest) share the longest international border between any two countries. Canada shares a land border only with the United States, while the United States shares a second land border with Mexico.
2. Russia – Kazakhstan border: (7,644 km)
Russia, the largest country in the world, borders 14 countries. Its longest land border, which is also the world’s second longest land border, is with Kazakhstan. It became an international border upon the dissolution of the USSR in 1991.
3. Argentina – Chile border: (6,691 km)
While Argentina is the 8th largest country in the world; Chile is much smaller in area. They share the third longest border in the world.
4. China – Mongolia border: (4,630 km)
We all know China is the third largest country in the world, and has total land borders of 22,147 km shared with 16 countries. China’s longest border is with its Northern neighbour, Mongolia.
5. Russia – China border: (4169 km)
Despite the fact that Mongolia and Kazakhstan stand between those two giant countries, they still share a mutual border long enough to be the 5th longest in the world. The currently valid agreement concerning the physical modalities of managing the China–Russia border was signed in Beijing in 2006.
6. India – Bangladesh: (4,142 km)
India is the 7th largest country in the world and third largest in Asia. It has its longest border with the small country of Bangladesh, which is around 5% of the size of India.
7. Russia – Mongolia border: (3,452 km)
Amazingly, three of Russia’s 14 land borders are among the world’s 10 longest land borders. And like Kazakhstan and China before, this border is also with a neighboring country to the south. As to Mongolia, it only has two land borders: with Russia and China, but both are among the longest in the world.
8. Brazil – Bolivia border: (3,403 km)
Brazil is the 5th largest country in the world, and shares a land border with 10 countries. Its longest land border is with Bolivia. The boundary line crosses a variety of terrains, going from large urban areas by inhospitable deserts and forests.
9. China – India border: (3,380 km)
This particular border happens to be China’s third longest land border and India’s second longest. The border is in more than a single section, and the main section is the “Line of Actual Control” around the Kashmir region which includes many disputed parts.
10. United States – Mexico Border: (3,155 km)
While the United States shares a land border only with Canada and Mexico, Mexico itself shares borders with the United States, Guatemala and Belize. This border is the most frequently crossed international boundary in the world, with around 350 million legal crossings every year.