Domesday Clock Still Ticking US and Russia almost started a nuclear war in Oct 1962 over Russia putting nuclear missiles in Cuba. President Kennedy invoked the Monroe Doctrine, the cornerstone of US foreign policy and had prepared to go to war. Russia backed down.
One of the key tenets of the doctrine is that the US will not permit colonization of countries in Western hemispheres and US will, in turn, not interfere in European wars.
Is history now repeating itself with Russia demanding Ukraine must not join NATO??
Let's not pour gasoline on the fire. You cannot judge what Putin will or will not do when his back is pressed to the wall.