2013. Yanukovich signed a mileston $10bn deal with Royal dutch shell to co-develop a massive gas field located in Eastern Ukraine.
This deal would have meant that Ukraine would have become a little richer, and Europe would have become a little less reliant on Russian gas.
Just before the coup, Yanukovich was presented with a choice. Sign the EU-Association agreement (which required Yanukovich implement a series of austerity measures, that would have been unpopular with Ukrainians) or accept a loan from Russia as well as considerable gas discounts (cheap gas - cheap energy - population is happy). What would you choose?
Unfortunately USA backed a coup, less than a year later and overthrew a democratically elected leader. There was a bit of hope, when the opposition and Yanukovich signed a deal, which was supposed to put an end to all the hostilities. But one of the "minority" oppositon leaders (Dmytro Yarosh) heading the far-right "nationalist" party (neo-nazis) refused to honour the agreement, andd continued with the violence. Yanukovich was threatened with death, unless he left Kiev.
Then there's the US-hand-picked interim government that launched a war against Donetsk and Lugansk, just because they wanted some autonomy.