Or even an electronic device capable of digitizing a sheet of paper and sending it over some communication system such as a phone line. It would make facsimiles of the original... I guess we could call it a facs machine for short?
I supposed one can use carrier pigeons or trained ravens.
Which means interception and time limits.
Send it with a person in a diplomatic bag. If it gets intercepted it will be an international incident and you'll know 100% of the time that you are compromised.
Fair enough. But it also imposes time limits for critical communication.
Yes and they may use other avenues when required. As much as I sing songs about incompetence and ineptitude of most government offices (of my country), they do have a knack to survive (or competing forces are just as inadequate, take your pick).