I mean if you want a more detailed explanation then sure. LPR and DPR are mostly ethnic Russians, and they wanted to separate from Ukraine after the nationalist coup in 2014. This resulted in a civil war with Ukraine regularly attacking civilian population in Donbas. This was openly reported by western media such as seen in this CNN clip, and in this French documentary.

We can also take a look at a few slides from this lecture that Mearsheimer gave back in 2015 to get a bit of background on the subject. Mearsheimer is certainly not pro Russian in any sense, and a proponent of US global hegemony. First, here's the demographic breakdown of Ukraine:

here's how the election in 2004 went:

this is the 2010 election:

As we can clearly see from the voting patterns in both elections, the country is divided exactly across the current line of conflict. Furthermore, a survey conducted in 2015 further shows that there is a sharp division between people of eastern and western Ukraine on which economic bloc they would rather belong to:

So, if you wanted to make comparisons with Gaza here then the closest analogy would be with Ukraine having the role of Israel and Donbas having the role of Gaza. Hope that helps clear things up for you.