The tension is palpable in Ukraine. After Russia’s recognition on Monday of two separatist regions of Donbass and the promise to send troops there – which has not yet been confirmed – the Ukrainian Security Council has called for the establishment of state of emergency in the country. He mobilized his reservists and called on his nationals to leave Russia . At the same time, Western countries, which have all denounced the actions of Vladimir Putin, have announced a first series of economic sanctions. L’Express offers a primer to have all the keys to understanding the crisis in Ukraine.