Iran/Pakistan either way Russians need water ports..thats what we are taught in out text books...but I am open to discussion
Think about it... ignore reality and everything... just be logical.
What would be the point of having a warm water port?
They have no sea lanes of communication or commerce to protect.
Is Afghanistan and Pakistan a barrier to trade with someone?
The US has found what Pakistan is like for a trade route to support its operations in Afghanistan and the Soviets would know the locals would be rather more hostile to anything they would transport to any port they might occupy.
Look at this map:
Keeping in mind that all the Turkmenistan and Kazahkstan and Azerbaijan and Uzbekistan are all Soviet republics exactly what makes an invasion and occupation of Afghanistan AND Pakistan easier than simply going down through Iran?
At the time Pakistan was Americas best friend in the region... in return for some free fighter planes and tanks and more importantly help against Iraq in the 1980s that the Iranians would have been happy to lease a port in southern Iran if the Soviets built a nice railway from the north of Iran down to the south... plus guaranteed support against the US... and perhaps civilian nuclear reactors 20 years early. (the Germans started in the late 1970s and most of the problems the Russians have had with the project is that it is half German design and half Russian.)
The main question however is WTF do they need a warm water port for? They have icebreakers that allow them to operate in cold water ports already... it is the west that needs lots of bases to protect its sea lanes like the convoys taking material from the US to Europe.
It is like western surprise at the bomber gap... they didn't understand why the Russians didn't have so many bombers or inflight refuelling aircraft to support those bombers.
The simple fact is that strategic bombing campaigns are a western thing.
The real reason for the Soviet conflict in Afghanistan was that the CIA... after success in Iran in undermining democracy and starting to pillage the resources of Iran decided to continue the same program in Afghanistan. The CIA was kicked out of Iran in 1979, which was also the same year that the Soviets went in to support the Afghans to protect them from an insurrection.
Very simply they wanted an Afghan government that was friendly to the Soviet Union and unfriendly to the US. The US wants the same thing in Cuba, and Mexico and central and south america. It has nothing to do with the cold war or expansionism, and everything to do with stable borders and happy neighbours.