I think I get it right. They are fed up with the official Ukrainian government forcing them to Westernize by joining the EU, when the people of Donbass speak Russian, not the same as Ukrainian, and want to identify with Russia as the great leaning-power rather than the EU. So, NATO along with the Ukrainian government has made military operations in Eastern Ukraine, where the ethnic Russians live and the Russian Federation is arming the secessionists.
I am sure I am right in general, but not in particular. Can anyone better-read than me verify/falsify this?