What is morally acceptable?

Yesterday I had a long and tricky discussion with some of my colleagues about the war in Ukraine. It was tricky because one of my colleagues suggested to consider Russian side before judging that it is not ok to invade Ukraine. While he wasn’t fully up-to-date with what is going on in this war as I am, he kept pressuring me to think that Ukraine might have done bad things in the past to justify Russian invasion. I find this point of view morally hard to hold and justify. Even if it is about joining NATO or not and the effects on Russian political posture and geopolitical posture, I cannot accept any justification.