Russia Ukraine war, page-233962

Civil war broke out "After" the Secession

That's what happened to all Civil Wars.

For example, the US civil war started after the South voted to secede. Even right now, the States can't secede without triggering a civil war.

So if No Secession, No Civil War.

As to atrocities, it happens in all wars - especially civil wars. That is why they introduced Rules of Wars - and Rules of Wars only minimize atrocities, not stop them - just look at what is happening in Israel and Palestine now.