Just to point out that 56% of the population in the Donbas before the war identifed as Russian speaking Ukrainians while 34% identified as ethinic Russian.

The east of the country was ruled by the Romanovs in the 19th century, while west was part of Austro-Hungarian empire for a long time.

Ukranians in the Donbas started speaking Russian, much like how Irish people under British rule rapidly stopped speaking Irish and switched to English in the 19th century, but they didn't stop being Irish.

There was also an immigration of Russians beginning in the 18th century, that population movement increased in the early 20th century because the mines were looking for workers.

Basically, it wasn't as black and white as portrayed by Russian propaganda. Russian speaker doesn't always mean ethinic Russian.

Ukraine didn't go into the Donbas with the intention of ethically cleansing the region of Russians, as explained the situation wasn't black and white, as many identified as Russian speaking Ukrainians.

Russia installed a number of pro-Russian milita leaders, some like Strelkov (involved in shooting down MH17) came from outside, from Russia. Russia stirred up, instigated and suported a separatist movement that Ukraine tried to resist, that was covertly suported by the Russian army. Strange for farmers and miners to find so many T-72s lying around. And, when it seemed that the pro-Russian militas were going to loose, the Russian military secretly invaded Ukraine and routed the Ukranian army.