The five unresolved separatist conflicts of the post-Soviet space in Eastern Europe are the biggest risk to Europe's stability and security. Four of these - Abkhazia, South Ossetia in Georgia, Transnistria in Moldova, and Nagorny Karabakh contested between Armenia and Azerbaijan - date back to around the collapse of the Soviet Union in 1991-2, and became called 'frozen conflicts'. The fifth is Ukraine's Donbas, which in 2014 saw large parts of...