Well, you kinda spoke against your own point there. Why would it concern the US, the Indian invasion of Pakistan? The Cold War included more sabotaging the other side, than improving your own side meaning = Pakistan wasn't held a puppet because the US needed it, but because USSR needed it.
India was one of the most important Soviet allies by the 70s. The Indian victory in the 1971 war greatly reduced American influence in South Asia, since they were now down to just West Pakistan.
Clearly, America was concerned by the Indian victory, because Nixon dispatched the 7th Aircraft Carrier Fleet to the Bay of Bengal. However, the Fleet was deterred by Soviet nuclear subs from Vladivostok.
If America thought that using an aircraft carrier strike force against India would be too much of a risk, there is no way in hell they would have attacked the USSR over Pakistan. In a WWIII scenario America would be facing a lot more than a couple nuke subs.
I don't know how do you imagine an invasion of Pakistan by the Soviets. They couldn't hold onto Afghanistan itself. Of course they could I mean, but it cost them so much that it sped up the process of USSR desintegration by at least 5-10 years. I personally don't think Afghanistan was worth the price Soviets paid, I think it's Brezhnev's fault, just like I would blame him the most for the USSR desintegration. He destroyed the ideology (no matter how compromised it already was) for the sake of USSR national interests - no wonder there were never any ideological spies in the 80s.
Back to the topic, I believe that invading any country as large as Pakistan was, is impossible in modern warfare. I don't think you can subdue a 100million country (roughly the pop of Pak back then), just by military. Who would the Soviets/India put their as the puppet government? Noone. Who could they put - noone. The communist movement there was non-existant, and I don't even want to mention what kind of "support" would a pro-Indian govt have in Pak. Also, any invasion of Pakistan would be that much harder by the fact it's much further than Afghanistan (oh and did I mention that supply lines would go through a hostile environment), and the fact that US would be able to ship unlimited resources via sea.
USSR could have a strong influence over Pakistan only in the case of their eventual victory in the Cold War. I percieve it as one of the most resilient could-be-invaded places by the USSR.
You bring up a valid point there. Even in the 80s Pakistan had a population of 90 million, which is no small figure. However, I never said that the Soviet Union/India would take over the whole country. Pakistan can be divided into roughly five regions: Punjab, Sindh, Balochistan, NW Tribal Areas, and Northern Areas.
The most populous of these regions - as well as the most fertile - is Punjab, which accounts for half of the population and one-fourth of the total area. The Punjabis are the dominant ethnic group in the Pakistani sociopolitical system. They make up 90% of the military and control the majority of political positions.
Sindh makes up about one-fifth of the total population and one-fifth of the area. The ethnic Sindhis make up about 60% of the population, and maintain a distinct identity. Since the 70s there have been conflicts between the Sindhis and the Mohajirs (Muslims from India who emigrated to Pakistan after the Partition). The Mohajirs make up 20% of the population and dominate urban economic activity in Sindh. The province is also home to nearly all of Pakistan's Hindus, who together form about 8% of the Sindh's population. Sindh is also home to Pakistan's only major port and largest city, Karachi.
Balochistan is by far the largest province, accounting for over 45% of the total area, but only about 5% of the population. The ethnic Balochis are mostly a nomadic people and are fiercely independent. In the 80s there was a very active independence movement in Balochistan (it is still quite active today), which was allegedly supported by India's intelligence agency, RAW. Regardless, the Pakistani central gov used heavy handed measures against the Balochi people, which gave Gen. Zia the title "Butcher of Balochistan". Balochistan is also notable for providing much of Pakistan's energy (through hydropower and natural gas) and making up most of Pakistan's coastline.
The NW Tribal Areas are similar in ethnic composition and geography to Afghanistan. The warlike Pashtuns are the dominant ethnic group here, and the society is tribal and deeply conservative. The Pakistani central gov has very limited control here.
The Northern Areas consist of Pakistani-occupied Kashmir (POK) and the agency of Gilgit-Baltistan. Both regions are claimed by India as part of Greater Kashmir. The Balti people of Gilgit-Baltistan are tribal and independent; recently there have been reports of a simmering rebellion amogst them against the Pakistani central gov. I don't know much about them in the 80s. As for POK, it is one of the most heavy-handed regions of Pakistan. Very little information comes into the region and very little comes out.
Coming back to topic, I envision the objective of a joint Indo-Soviet invasion to be the further partition of Pakistan and the occupation of strategically important areas, NOT the complete conquest of the country. Military interventions in Sindh and Balochistan can easily take these areas out of Islamabad's grasp. Pro-Soviet and pro-Indian governments can be established in both regions, which will give the USSR their dream of direct access to a warm-water port in the Indian Ocean (Karachi). As for the NW Tribal Areas, the Pashtuns have long desired a united nation for all their people, to be named Pashtunistan. This country can be created using Pakistan's NW Frontier Province as well as the eastern parts of Afghanistan. And finally, the Northern Areas will go to India, which will complete the reunification of Kashmir. The only region to remain part of "Pakistan" will be Punjab, which will be left without access to any ports and deprived of energy, making it extremely dependent on India and Indo-Soviet puppet states.
Thus, the permament castration of the ill-concieved state of Pakistan would be complete.
Also, keep in mind that the geography of Pakistan would lend itself to Soviet tactics much more than Afghanistan. The Red Army was trained to fight on the plains of Eastern Europe, not the deserts and mountains of Afghanistan.
