I believe the theory realism comes close to explaining the annexation of Crimea, the theory falls short compared to Constructivism. Russia’s president Putin decision to annex Crimea is in accordance with the constructivist view point. Putin shows numerous efforts of self-interest and ability to be constructive and change things to benefit his state. With the use of his strong military presence he gains cooperation with other states and land, especially with the Northern Sea Route. Russia exercises three quarters of its Navy and large forces of ground troops, to protect the Northern Sea Route and use it for their gain. Putin's self-interest shows because he is fulfilling his countries natural resources despite the turmoil the country was in.
