Approval by one parliament may make the action legal within Russia but it does not make an invasion legal under international law. The Russian parliament has no legal authority over Crimea or other regions of Ukraine so cannot authorise the use of troops within that country – that is something only the Ukrainian parliament, or in extremis the UN Security Council can authorise.  Similarly the Crimean parliament cannot legally simply decide that Crimea is no longer a part of Ukraine, even a referendum does not enable such a transfer of sovereignty. Self determination should be internal, not external. [1]  [1] Supreme Court of Canada, Reference re Secession of Quebec, [1998] 2 S.C.R. 217