Found this great explanation on Reddit, hope that it will help you understand. Link to comment on Reddit.
“The version I’ll tell is controversial, but the most accurate.
Russian President Vladimir Putin has envisioned a return of Russia to superpower status. In order for the now re-energized nation to do this, it must win influence within, and expand, its existing sphere of influence. Putin, a former KGB officer, has even been on record despairing over the loss of the Soviet Union.
But the growth of Russia’s sphere of influence is limited, at the time being. Russia has virtual control over the central Asian nations, but is territorially checked to the south by India, to the Southeast by China, and to the west by both NATO and the EU.
If you remember the 2008 South Ossetia War between Russia and Georgia, you may remember the cause of the conflict: Russia’s desire to “protect” South Ossetians and Abkhazians who may be Russian citizens, although that statistic is very low. The war with Georgia came at a time when Georgia was attempting to enter NATO.
NATO, being an international alliance established with the very intention of countering the combined forces of the Warsaw Pact nations, now finds itself opposing Russia. However, the threat from Russia upon Georgia is now too great, and by engaging Georgia, Russia has also removed Georgia’s ability to join NATO. NATO does not want to risk such a certainty for all-out war with Russia should they attack a Georgia that’s in the organization, and Russia does not want anymore NATO members sitting on her bordersand preventing the growth of the Russian Federation in land and both political and economic influence.
Fast forward six years to today – 2014. Ukraine, finding itself in economic straits and having elected a pro-Russian government, has fielded offers for economic aid in the form of loans from both Russia and the EU. Now, whoever Ukraine borrows from also inherently buys into that entity’s influence, as well. The government of Ukraine wanted to accept the Russian offer (and had already partially done so), but many of the people there were pro-EU.
This is where the protests began. Peaceably, hundreds of thousands of Ukrainians, mainly in the pro-West western and central areas of Ukraine, attempted to protest, but were (arguably) both fired upon and denied their right to protest. Allegations of both murder and torture of protesters sprang up, and the protests became violent.
Now, it is (controversially) worth mentioning that as this stage was unfolding, a Russian intelligence ship docked in Havana. At the same time, Russians, under the premise of defending Russian-speakers in Crimea, have secured the Crimean peninsula, in violation of the 1994 Budapest Memorandum. Essentially, Russia has taken advantage of the large Russian-speaking population of Crimea, as well as the presence of the Russian naval base at Sevastopol in Crimea, to actively engage the Ukrainian government.
Currently, the Russians have not ruled out a full-blown invasion and dismantling of Ukraine. The Duma (Russian parliament) has at least considered legislation which would more easily allow for the annexation of at least parts of Ukraine.
So, to recap, as it stands, Russia is eyeing its pro-West neighbors, most of them former Warsaw Pact nations, and wanting to bring them down a peg without risking all-out war with NATO. With Belarus virtually on board with a revival of a Russian superpower, this left the rebellious Ukraine as the only frontier country left that was neither pro-Russia or a NATO member.”
by Reddit Commentor murder_cheese