The cause of the war is a paranoid, criminal, tyrant who has no regard for human life.
Ukraine made a mistake to actively push for NATO (can I say that word?) and EU membership but that is not a pretence for an invasion.
This is a nation who has fought for independence and democracy for decades. They have the right to make their own decisions without the threat of invasion from a scumbag like Putin.
Read a book. Go and see how Russia has treated Ukraine over the centuries. They have a right to want to get away from that and move towards a more democratic society.