The liberals just think that there are inherently evil people like story book villains who have to play the role by throwing a wrench in what would otherwise be a perfectly peaceful and happy capitalist world order since that’s what antagonists do. It’s a form of Great Man Theory; everything would be fine if it weren’t for the bad guys, in this case Putin, who just want to take over for the sake of their own personal vanity. There doesn’t need to be any reasons for the war beyond that for liberals. It’s only materialists who have to worry about looking for material causes of things.