After some militants in those areas and minorities including the Russian-speaking Ukrainians there that turned that region into a war zone which is why Russian steps in to make it peaceful.
If Ukraine wants to turn that region into a bigger warzone like your whole country, be a member of NATO and you will see what's left for the country. It's never worth bringing a 3rd party that will take everything instead because after all both country was part of the USSR and your NAVY shares that Crimea sea.
Sorry, but now, either intentionally or out of ignorance, you are carrying informational nonsense!
Yanukovych only negotiated that Ukraine allows Russia to prolong the agreement on the lease of certain territories for the needs of the Russian Navy, But no more!
I will also add that according to this agreement, the Russian Federation was obliged to coordinate any exit of the Russian military personnel outside the territory of the leased bases - no free movement outside the leased zones. And yet - in Ukraine there is a PARLIAMENTARY-presidential power, and the president cannot make any decisions unilaterally. Everything I have said can be checked in the legislation of Ukraine and open agreements of the Ministry of Foreign Affairs of Ukraine.
And about the "militants" - without organization, funding, direct support, including by the regular troops of the Russian Federation, nothing would have happened. I have been working with the eastern region for many years, and Donetsk "I know like the back of my hand", and I know that since 2004-2006 there has already been a pumping of pro-Russian ideology. population, Russian Cossacks, Russian propagandists. You can’t even imagine what kind of nonsense you pumped them up. But this is exactly how the propaganda of the Russian Federation works - the search for marginalized, degrading individuals, brainwashing, hammering into the head the image of the enemy who is to blame for all his troubles, and of course these enemies became pro-Ukrainian citizens, and of course the degrading population of Donbas was hammered into the head that they were the ones created all the values in Ukraine and fed the rest of the country, although in reality they were one of the most subsidized and plundered regions.