The atomic bomb. Hear me out on this.
The invention and production of the atomic bomb marked the largest and most diverse collaboration of effort from science, industry and government under the worst possible conditions, resulting in 70 years of unprecedented relative peace. Nothing else comes close.
Science & Academia - Nuclear fission was made possible by incredibly advanced scientific research that took place over decades in various countries' universities, with contributions from scientists of incredibly diverse backgrounds, including women and German Jews. The international collaboration, especially between Britain and the US was like nothing that had ever been seen before.
Government - Today, we know the US government to be a gridlocked, partisan joke incapable of getting even basic things right, but the Manhattan Project was a shining example of the government working in its highest gear. Not only did the government (most specifically, FDR), listen to the eggheads about the possibility of nuclear weapons, it executed extremely well on two fronts: 1. Building a bomb of our own and 2. militarily disrupting the Nazis' ability to produce their own.
My favorite story from the book The Making of The Atomic Bomb was one about a production issue at Oak Ridge. The scientists gave the head of the Manhattan Project, General Leslie Groves, a list of materials needed to build the factories and centrifuges for the bomb. One item on the list was a massive industrial quantity of copper. Groves told the scientists: "Um. We don't have anywhere near that much copper. There's a war on, you know? Is there anything else you can use?" The scientists said "Not really. Theoretically we could use silver, but coming up with several hundred tons of silver would be impossible."
Groves, with carte blanche in hand, contacted the US Mint and was able to get (IIRC) ~$600 million dollars worth of pure silver trucked down to Oak Ridge and melted into the necessary equipment.
Industry - I don't have any specific examples, but the Manhattan Project was an industrial project of immense scale, conducted in several different states (TN, WA, NV, NM, etc). The government relied heavily on advancements in myriad industries from finance to construction to shipping to get it done. And, BTW, it was American industry that supplied Europe before the US entered WWII and the military during the war, which kept the Nazis' bomb development off track and the homeland untouched.
Military & Intelligence - As soon as the metaphorical nuclear alarm was sounded by top officials, the intelligence community kicked into overdrive to find out about and disrupt German nuclear production in every way possible, from plotting to kill Nazi scientists to sabotaging a heavy water facility in Norway.
http://www.nytimes.com/1993/02/28/world/new-book-says-us-plotted-to-kill-top-nazi-scientist.html http://en.wikipedia.org/wiki/Norwegian_heavy_water_sabotage
All of this was done in secret, during the worst war in human history. In the 70 years since, there have been no further outbreaks of all-out global war and casualties from war have dropped dramatically.
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Many more of the baby boomers would have been killed in WWIII (the global war against communism) than died in Korea and Vietnam had nuclear weapons not assured mutual destruction.
