Some large pieces of evidence. 1) It happened before. 2) Russia literally invaded its neighbor and is waging a war of imperialist aggression. 3) Putin just publicly reiterated one main justification for the war is that Ukraine is not a real nation. Then said Poland and the Baltic states are not real nations. I'm not convinced Russia or Putin will be that stupid but rather than no evidence as you claim there is certainly enough evidence to be worried and on guard.