Pervez Hoodbhoy in The Express Tribune:
Once upon a time Iran was Pakistan’s close ally — probably its closest one. In 1947, Iran was the first to recognise the newly independent Pakistan. In the 1965 war with India, Pakistani fighter jets flew to Iranian bases in Zahedan and Mehrabad for protection and refuelling. Both countries were members of the US-led Seato and Cento defence pacts, Iran opened wide its universities to Pakistani students, and the Shah of Iran was considered Pakistan’s great friend and benefactor. Sometime around 1960, thousands of flag-waving school children lined the streets of Karachi to greet him. I was one of them.
The friendship has soured, replaced by low-level hostility and suspicion. In 1979, Ayatollah Khomenei’s Islamic revolution, and the Soviet invasion of Afghanistan, set major realignments in motion. As Iran exited the US orbit, Pakistan joined the Americans to fight the Soviets. With Saudi money, they together created and armed the hyper-religious Pashtun mujahideen. Iran too supported the mujahideen — but those of the Tajik Northern Alliance. But as religion assumed centrality in matters of state in both Pakistan and Iran, doctrinal rifts widened.
These rifts are likely to widen as the US prepares for its withdrawal from Afghanistan. Iranians cannot forget that in 1996, following the Soviet pullout from Afghanistan, the Taliban took over Kabul and began a selective killing of Shias. This was followed by a massacre of more than 5,000 Shias in Bamiyan province. Iran soon amassed 300,000 troops at the Afghan border and threatened to attack the Pakistan-supported Taliban government.
More here.