A detailed look at how Russia annexed Crimea
A year ago, the Ukrainian peninsula of Crimea was "reunified" with Russia by way of well equipped, organized, and trained "self defense units" who were actually Russian special forces.
The operation to seize Crimea began on February 27, 2014 when an unidentified task force captured several government buildings including the parliament in Simferopol.Within a month, Putin signed a treaty to annex Crimea and has since then turned the peninsula into a Russian forward operating base.
The following map from the International Institute for Strategic Studies documents Russia's encroachment on Crimea:
During a celebratory speech earlier this month, Russian President Vladimir Putin acknowledged that the mountain of criticism and economic sanctions placed on his country for the illegal annexation of Crimea were creating difficulty for Russia.