When the USSR brought missiles to Cuba, the Cuban Missile Crisis happened and almost a war broke out.
When NATO in 2020-2021, taking advantage of Zelensky's inexperience, began to approach a country 400 km from Moscow, the Kremlin repeatedly warned, "don't cross the red line", this is unacceptable for Russia. But this did not stop the USA.
And now in the place of the USA'1962 there is Russia, and in the place of the USSR'1962 - the USA. And the Northern Cuban Missile Crisis - 2 developed.
And all the talk about "protecting democracy" is a smokescreen. The Kremlin has repeatedly stated that Ukraine can join the EU as many times as it wants, but Ukraine's participation in NATO is unacceptable from the point of view of the national security of the Russian Federation.
And do not write about sovereignty - Cuba also had it in 1962, but this did not stop the USA in any way.
And there is no need to write about humanity - no humanity prevented the US from dropping 2 nuclear bombs on the heads of Japanese children.
As US state dep says "nothing personal, just interests of national security"... and starts intervention on another continent. Why you wonder what Russia now follows own interests of own national security, at least Ukraine is just behind Russian border and not somewhere in the Afghan mountains, or Syrian desert.