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Stopped one of the most evil empires in human history -- in which over 30 million humans were slaughtered by their own leader, in which no one had any rights and could be murdered, raped or tortured with impunity. (USSR)
Paid Europeans and Japan and Korea (even our former enemies) to rebuild themselves. The other great victor of WWII -- the USSR -- raped their former enemies and murdered their people.
Enforced the law of the seas and created (along with our British cousins) a system of legal shipping and trade that permitted the prosperity you have right now.
Protected half of humanity at our cost, allowing them to skimp on their defense budgets and spend that money at home on health care, education and infrastructure -- thus allowing them to swim in wealth and transparency on a level never before seen in human history.
Act as the primary (though not sole) engine of invention of the last 75 years, contributing more technology and wealth to the planet than any one, two or three nations currently in existence.
We're having this conversation on a series of technologies and programs that are so overwhelmingly American (with notable contributions from Europe) that it's almost disgusting in its disproportion.
Provide the most entertainment in the form of movies, TV and music comparable only to our cousins across the pond, the Brits. Go anywhere on this planet, and you're guaranteed to see an American musician, performer, TV show or movie.