Mutually Assured Destruction from The Office
Dwight and Jim have a brief interaction that perfectly sums up the basic idea of mutually assured destruction, or MAD. In the episode, Jim is having a frustrating day missing Pam and trying to connect with her over the phone and video call, and he just can't do it for all the distractions in the office. Finally, tired of being hassled by his coworkers, Jim asks Pam during a phone call to switch to instant messaging so he can have a private conversation about his big lunch plans (spoiler alert: he's going to propose at the gas station. It's your fault if I somehow ruined that for you nearly a decade later).
Naturally, Dwight, being the authority worshiper he is, antagonizes Jim and tries to get him to share what he's typing in his chat with Pam. Obviously, Jim demurs. It's at this juncture that we get into a true deterrence dynamic. The next three lines summarize the entire concept of mutually assured destruction.
Dwight: "I'm gonna write you up for not working." Jim: "I'm gonna write YOU up for not working." Dwight: defeated but respectful expression "Fine. Neither of us will write the other up for not working."
This exchange perfectly encapsulates nuclear deterrence in terms of real threats and consequences and the way nuclear weapons can or can't be used to influence the behavior of others. For Dwight, bringing down the full force of bureaucratic machinery onto a coworker is the equivalent of going nuclear. He reveres punishment and authority, and he believes everyone else has the same fearful adoration for the might of company policy.
Accordingly, he believes he can wield his own authority as Assistant (to the) Regional Manager to coerce people into complying with his demands. We see that throughout the entire series, and in this case he is turning it on Jim to get him to reveal what he's saying in a private conversation.
For Jim, things are completely different. He has no reverence for corporate machinations and no respect for Dwight's "authority." At this point, he just wants quiet and privacy so he can connect with his beloved. His frustration is at a peak, and he's in no mood to tolerate shenanigans (not so fun from the other side, is it Jim?). He's tried everything else to get Dwight and others out of his space, and it isn't working. Dwight's last attempted incursion into his DMs with Pam is the last straw. His only choice is to respond with proportionate force.
The immediate, equivocal threat Jim issues Dwight strikes a humorous chord because the audience knows just how differently these two characters view authority. Dwight's adolescent love of formalized punishment results in what Dwight thinks is the ultimate threat, but that means nothing to Jim, especially coming from Dwight.
But if Jim doesn't give some kind of response, he knows Dwight will just continue to pester him and hold the (foam) sword of Damocles over his head. Jim returns the threat exactly in kind, actually word-for-word in a true how-the-turn-tables moment, even though he, Jim, knows it's a meaningless threat.
The important thing is that Dwight thinks it's real, credible, and would result in unacceptable damage to himself. He sees that now that the biggest weapons are drawn on both sides, the dynamic turns into an impasse.
Jim is allowed to continue doing what he's doing without Dwight's threats, even though in Dwight's eyes both he and Jim will suffer the ultimate consequence, because although he gets his wish to punish Jim, suffering that punishment himself is an unacceptable risk.
MAD in the real world
Although it's a bit more complicated than that, in reality, mutually assured destruction is essentially the same situation. During the Cold War, the U.S. and Russia each had enough nukes to completely, and quite literally, wipe the other off the face of the map.
At various points, both countries had tens of thousands of nuclear warheads sitting on missiles or loaded into airplanes ready to deliver to any one of hundreds of targets in the other's national landmass.
Russia wouldn't dare fire a nuke at Hawai'i, even though it might think there'd be a strategic advantage to attacking the military assets there, because they knew that would result in at least as big a shot from the U.S., and might even result in a nuclear missile landing right in the heart of Moscow.
That's definitely not a trade the Russians would have accepted. The same is true in the other direction: The U.S. wouldn't have fired at strategic locations in the Baltics in exchange for the destruction of New York or Washington or LA. The punishment is just too harsh to justify.
That hasn't always been the case throughout history. We have lived in a nuclear world for more than 75 years, and the effects of deterrence are well-understood and taken as a given at this point. But before 1945, if a country wanted to punish an enemy and force it to comply, it first had to defeat that enemy in war, or at least gain enough ground invading the territory that the enemy had no choice but to obey.
Bullying on the international scene was much more costly and difficult because of the enormous amount of resources it took to influence even smaller, weaker states. Even the greatest generals, like Napoleon, learned that eventually, a nation's power ran out once it got too far from home.
Nuclear weapons changed all of that. The bomb is so powerful, so dangerous, so utterly devastating compared to other weapons of war, that even merely possessing it was enough to give a country power. If you could deliver a nuclear bomb with any reliability, suddenly you were able to deal an immense, unacceptable amount of punishment out to adversaries, and this is the key bit, you didn't need to fight or win a war first in order to do so.