Where one country ends and another begins is sometimes a thin line on a map and sometimes a frontier thousands of kilometres long. The longest land borders on Earth stretch across deserts, mountains and rivers, shaping trade, migration and history. Here is how the ten longest rank.
| Rank | Border | Length |
|---|---|---|
| 1 | Canada – United States | 8,893 km (5,525 mi) |
| 2 | Russia – Kazakhstan | 6,846 km (4,254 mi) |
| 3 | Argentina – Chile | 5,300 km (3,293 mi) |
| 4 | China – Mongolia | 4,677 km (2,906 mi) |
| 5 | India – Bangladesh | 4,053 km (2,518 mi) |
| 6 | Russia – China | 3,645 km (2,265 mi) |
| 7 | Russia – Mongolia | 3,543 km (2,201 mi) |
| 8 | Brazil – Bolivia | 3,400 km (2,112 mi) |
| 9 | China – India | 3,380 km (2,100 mi) |
| 10 | United States – Mexico | 3,141 km (1,951 mi) |
1. Canada – United States: 8,893 km (5,525 miles)
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The longest international border in the world runs between Canada, the world’s second-largest country, and the United States. It crosses the continent in two stretches, one between Alaska and Canada’s Yukon, and another along the lower 48 states.
2. Russia – Kazakhstan: 6,846 km (4,254 miles)
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Russia has more land border than any country, over 20,000 km shared with 14 neighbours, and its longest single frontier is with Kazakhstan, the largest landlocked country in the world.
3. Argentina – Chile: 5,300 km (3,293 miles)
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Chile is far smaller than Argentina, but its long, narrow shape stretched along the Andes gives the two countries the longest border in the Southern Hemisphere.
4. China – Mongolia: 4,677 km (2,906 miles)
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China shares borders with 14 countries, and its longest is with Mongolia to the north, a vast and sparsely populated nation wedged between China and Russia.
5. India – Bangladesh: 4,053 km (2,518 miles)
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India almost wraps around Bangladesh, and the border was once famously complex, broken into nearly 200 segments by tiny enclaves until a 2015 land-swap between the two countries finally simplified it.
6. Russia – China: 3,645 km (2,265 miles)
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Even with Mongolia and Kazakhstan between them, the two giants still share one of the world’s longest borders, divided into a long eastern section and a short western one.
7. Russia – Mongolia: 3,543 km (2,201 miles)
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Three of Russia’s borders make this top ten. Mongolia has only two land neighbours, Russia and China, and both rank among the longest on Earth.
8. Brazil – Bolivia: 3,400 km (2,112 miles)
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Brazil, the largest country in South America, touches ten neighbours, and its longest border runs with Bolivia through the Amazon basin and the Pantanal wetlands.
9. China – India: 3,380 km (2,100 miles)
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This Himalayan frontier is among the most disputed on Earth, much of it marked only by the contested Line of Actual Control rather than a settled boundary.
10. United States – Mexico: 3,141 km (1,951 miles)
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The most frequently crossed border in the world, with hundreds of millions of legal crossings a year. Much of it is walled, fenced and monitored with sensors and cameras.
For more world geography, see the largest countries in the world, the largest islands in the world, and the deepest lakes in the world.
