In December 1979 US president Jimmy Carter wrote to Soviet leader Leonid Brezhnev, protesting the Soviet Union’s military incursion into Afghanistan:

Dear President Brezhnev,

“I want to ensure that you have fully weighed the ramifications of the Soviet actions in Afghanistan, which we regard as a clear threat to the peace. You should understand that these actions could mark a fundamental and long-lasting turning point in our relations. Taken without any previous discussions with us, they constitute in our view a clear violation of the Basic Principles on Relations which you signed in 1972.

My government can in no way accept the Soviet Government’s explanation, conveyed to Ambassador Watson on December 27th, that Soviet military forces were sent into Afghanistan at the request of the leadership of that country. The facts of the matter clearly show that these same Soviet forces were employed to overthrow the established government of Afghanistan and to impose a new government, which has brutally executed the former President and, reportedly, his family.

Large-scale movements of military units into a sovereign country are always a legitimate matter of concern to the international community. When such military forces are those of a superpower, and are then used to depose an existing government and impose another, there are obvious implications both for the region and for the world at large. We note with the utmost seriousness that this is the first time since the invasions of Hungary and Czechoslovakia that the Soviet Union has taken direct military action against another country. In the present instance, the Soviet military intervention in Afghanistan—a previously non-aligned country—obviously represents an unsettling, dangerous and new stage in your use of military force, which raises deep apprehension about the general trend of Soviet policy.

We are pledged not to exacerbate conflict fraught situations and to consult when threats to the peace arise. If these mutual obligations are to have any meaning, then they must obviously include a refusal by the superpowers to engage in armed combat except as a very last resort and then only in legitimate self-defence. Because our interests are global, we must recognise that actions taken in one area have a spill-over effect in other seemingly unrelated areas, as well as in that area itself.

Neither superpower can arrogate to itself the right to displace or overturn a legally constituted government in another country by force of arms. Such a precedent is a dangerous one; it flouts all the accepted norms of international conduct. Unless you draw back from your present course of action, this will inevitably jeopardise the course of US-Soviet relations throughout the world. I urge you to take prompt constructive action to withdraw your forces and cease interference in Afghanistan’s internal affairs. Many years of promoting more stable and productive relations between our two countries could well be undermined if this situation is not resolved promptly.”