It's because of mutually assured destruction. It's the same reason why there's a tacit agreement between enemy heads of state to not just assassinate each other

It's because of mutually assured destruction. It's the same reason why there's a tacit agreement between enemy heads of state to not just assassinate each other. Doing so would just start a new world order that wouldn't be in anyone's interest. Sort of like nuking an enemy isn't a good idea either because of the retaliatory consequences it would necessarily cause.