The enclave of Nagorno-Karabakh is a powder keg at the centre of a decades-old dispute between Armenia and Azerbaijan. Its people are mostly Armenian, but under the Soviet Union it was ruled by Azerbaijan. In 1991, Nagorno-Karabakh declared itself independent. A three-year war followed, killing around 30,000 people. A fragile truce still holds, but Armenian forces occupy large swathes of Azeri land, and oil-rich Azerbaijan says it will take back the territories by force if there's no peace deal.