It is an invasion without Security Council sanction  The legality of Russia’s invasion of Crimea is simple “Russia’s military intervention in Ukraine violates international law.” [1] The UN Charter is unambiguous “All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state”. [2] Russia has both threatened the use of force by its parliament authorising the President to use force on Ukrainian territory [3] and actually done so by sending troops into Crimea. The only legal way for the UN Charter’s prohibition on force to be avoided is through a Security Council mandate. Which Russia does not have. [4]  [1] Posner, Eric, ‘Russia’s Military intervention in Ukraine: International Law implications’, ericposner.com, 1 March 2014  [2] United Nations, ‘Article 2’, Charter of the United Nations, 26 June 1945  [3] RT, 1/3/2014  [4] Deeks, Ashley, ‘Russian Forces in Ukraine: A Sketch of the International Law Issues’, Lawfare, 2 March 2014