Clo:
Just as the Soviets overstepped their bounds by putting missiles in America's backyard (Cuba) in 1962 leading to an extreme military response by John Kennedy, the West via economic imperalism in Ukraine has overstepped it's bounds, threatening Russia's security, economy, and strategic position on the Black Sea. This in combination with America's other foolish adventures in Russia's neighborhood; Afghanistan, Iran, Iraq, Syria, and Moldova.
I'm only surprised by a weakened Russia's restraint in addressing these activities, but Russia will risk a world war over Ukraine.