Call of Duty Modern Warfare 3 is my 24 year old Nephew's favorite game.  In it Russians invade Manhattan.  When I was a kid, suffice it to say, the Russians were not to be played with...except in games featuring nuclear war.  People not that much younger than me are totally disconnected from that reality.  At the beginning of Call of Duty's story mode New York City has been invaded by Russian forces.   As my father and I watched him we could not help but comment at how unrealistic that was.  Far less provocation than that would have lead to us nuking Russia, not a fire fight.  I hope that they get that on an intellectual level, as something they read about in school, there still seems to be a disconnect there.  (Update: I am not the only one that noticed how headache inducingly absurd some of the story mode of this game is. )    
Specifically I was reminded of an event known as Able Archer 1983.  If you are a young person and want to understand some of the fear and loathing that pervaded every day life back then I highly recommend you watch the following.  A very good documentary by the BBC which gave a bit of the feeling of what the 80's were like.)



In brief.
Various events in the early 1980's made the Soviet leaders so nervous about US intentions that a military exercise was almost misinterpreted as the prelude to an actual attack.  In response to the radio traffic generated by exercise Able Archer in 1983 the Soviets placed all their strategic forces on their equivalent of Defcon 2 alert.  Pilots were in their bombers engines started and right by the runways.  Nuclear ballistic missile subs were ordered to sortie.   Soviet ICBM's were placed on high alert.  All of this because of a exercise..not one shot had to be fired for nuclear war to start.

So when your sitting there fighting the Spetznaz in Lower Manhattan, and your older relatives have a good chuckle at that scenario remember this.  Everyone older than 25 has lived and been aware of a fear and danger that makes even a actual invasion seem like peanuts.  We lived through a time when destruction that must seem utterly unthinkable to you young folks was a very real threat.  

The man made extinction of our species. More people need to know about this.  

P.S.  We still have thousands of strategic nuclear weapons pointed at Russia, China, and other countries for reasons that hardly deserve to be called reasons.