5. Cambodia and Thailand The length of the border being 500 miles, dozens were killed and tens of thousands displaced on both sides of the border over the 11th-century Preah Vihear dating back to colonial times.
Thailand says the area was never drawn and the demarcation by the French in the beginning of 20th century lacked clarity.
After a long battle the, International Court of Justice awarded the Hindu temple to Cambodia.
But the dispute over the 1.8-square-mile area around the holy site has never been resolved.
An agreement was reached in December 2011, in which Thai troops had to withdraw from the disputed area.