Well, I was about to 'thank' you for the excellent question until I read the ridiculous article included in the OP.
Is invading Ukraine like Hitler starting WW2 (in Europe)?
What an amazingly, ridiculous comparison.
Hitler wrote his plans in Mein Kampf for all the world to see.
He wanted to conquer Poland and the Soviet Union for German 'living space'.
His invasion was for no other reason than pure, empire building built on 'Nordic' superiority.
Also, Hitler knew that to attack Poland would guarantee war with France and Great Britain as they had a mutual defense treaty with Poland.
Plus, knowing how the Nazi's treated Jews even as early as 1939 AND knowing that here was a large, Jewish population in Poland? Certainly the world could expect that millions of these Jewish Poles would be treated horribly - at best.
Putin - assuming he means what he says - is trying to stop a war in the Donbass that has killed thousands of people on both sides since 2014. And - I assume - the only way he believes that can be done is to remove the current leaders of Ukraine.
And there has been no external involvement - militarily - in the conflict thus far. Nor does it appear there will be.
Now I do not agree at all with Putin attacking/invading Ukraine proper (outside of the Donbass region).
But comparing that to Hitler declaring war on Poland is sheer nonsense.