For me it was World War II.
A great many of my relatives fought in that war and the military became a big part of our family culture.
After the war, and probably most important, my father and uncle used the GI bill to be the first men in the family to go to college.
This permanently raised the status of the family from poor farmers and ranchers to professionals.
I grew up in the Cold War under the shadow of nuclear warfare- another legacy of WWII.
I make my living in computers and networking- another technology that born (or grew exponentially) out of WWII.
Even though I was born 17+ years after the war, I can think of no other historical event that had its impact.
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What historic event most shaped your world?
I'm curious to see what you think and your reasoning behind it.