https://en.wikipedia.org/wiki/First_Battle_of_Donetsk_Airport
https://en.wikipedia.org/wiki/Second_Battle_of_Donetsk_Airport
these are major events that escalated the fighting between Russia and Ukraine, before that it was mostly the Ukraine fighting the poorly equiped 'pro-russian rebels' and bombing their own cities and utility services like water purification plants in the east of the country to force the population out