Mechanically I guess it would be seeing the end of pickers, corncribs, & shellers.

Lifestyle I'd guess air conditioning. But the funny thing was, like a lot of other things in life, who knew what they were missing? My 1st a-c car was in '76...but 1st a-c tractor was '73.

World-wise I'd have to say the end of the cold-war. Can anyone here explain to 10 yr old kids about the necessity of monthly atomic bomb drills in school? Many of our world-wide military bases became only memories for reunions after the fall of the Berlin wall.