Ukraine, formerly part of the Soviet Union, and the bulwark between Russia and Europe, was always going to be complicated.
The country is divided - ethnic Russians and Russian speakers who favour president Viktor Yanukovych, and Western-leaning Ukrainian speakers who support becoming part of the EU.
Here, as simply as possible, is the lead-up to the Ukraine-Russia crisis. Yes, we know it's more complicated than this, and more stuff happened. We refer you to the title of 'Idiot's Guide'.