Since its foundation in 1947 Pakistan has been a close partner of the Western bloc, cooperating militarily with both Britain and the United States. The country has long been a recipient of U.S. military aid and relied heavily on American arms, initially as a counterweight to both Soviet aligned India and to China in the 1950s. During the Soviet war in Afghanistan in particular the country was a critical asset for the United States, shooting down Soviet and Afghan jets and arming and funding the Islamic Mujahideen insurgents alongside the CIA to undermine the USSR's war effort and destabilise the Soviet backed government of Afghanistan. With Iran having turned against the U.S. in 1979 following the Islamic Revolution, Pakistan became the most effective conduit for U.S. arms to reach insurgents in Afghanistan.
Since the end of the Cold War Pakistani-American relations have cooled significantly, particularly since the killing of Osama Bin Laden by U.S. forces which entered Pakistani airspace for the operation illegally without informing the country's government. Many in the U.S. intelligence community also suspected that Pakistan had been aware of Bin Laden's whereabouts, particularly considering his residence near major military facilities. It was widely believed that Pakistan was holding the leader of Al Qaeda as a bargaining chip - rather than handing him over to the Western bloc as would be expected of a reliable partner. Pakistan's growing ties with China, including extensive military and economic cooperation, have also contributed to a worsening relations with Washington - which no longer views the country as a reliable asset against is adversaries as it had once been. With China replacing the USSR as the United States' primary adversary, it was inevitable considering the nature of Washington's foreign policy that ties with Pakistan would become strained unless the South Asian state revised the nature of its ties to China. The result has been that the U.S. has cut military aid drastically since 2015, and is highly likely to make further cuts or halt aid entirely in future.
Highly symbolic of the deterioration in relations between Washington and Islamabad has been the end of what had been high level cooperation between their Air Forces. Pakistan was the second foreign recipient of the F-16 after Israel, and following the cancellation of Iran's order in the aftermath of the 1979 overthrow of its U.S. aligned Shah which led to fighters initially marked for Iran to be diverted elsewhere. The F-16 remains the mainstay of the Pakistani Air Force, and though it is only a light platform it is the country's more formidable fighter and has been used to great effect as a result of the country's high levels of training. Relations today however bear a sharp contrast to the 1980s, and relations with the U.S. have deteriorated leaving the country unable to obtain the fighter from the U.S. as before. The result is that Pakistan has been forced to look to Turkey and Jordan to procure second hand F-16 fighters. The country has also manufactured its own fighter with extensive technical assistance from China, the JF-17 Thunder, which is a low cost light fourth generation multirole platform similar to the F-16 in its role. More recently however, Pakistan has turned to Russia for potential aircraft acquisitions, an unprecedented step which would have been considered unthinkable just ten years prior. The Pakistani Air Force has in 2017 entered consultations with Russia to purchase some of its latest fighters. With India's acquisition of a vast fleet of Su-30MKI advanced air superiority fighters, with capabilities well in advance of anything fielded by Pakistan which lacks any form of air superiority platform, it is possible that Pakistan is seeking a fighter to negate India's advantage. With the United States unlikely to provide the country with air superiority platforms, something it has only provided to four of its closes allies - Israel, Saudi Arabia, Iran (Shah era) and Japan - and with China restricted in its ability to export its J-11, Russia appears the only potential supplier of such a platform.
Pakistan has already signed deals on engineering procurement and for Russian engines for the JF-17, as well as having been provided with military attack helicopters. 2016 meanwhile saw the first joint military drills between the countries take place. Should Pakistan purchase Russian fighters, the Su-35 air superiority fighter being one prominent possibility, it would be a landmark in their relations and likely a final nail in the coffin of the country's special military relationship with the United States. A similar trend can be observed on the ground, with Pakistani tank divisions today comprised of Al Khalid tanks build with Chinese assistance, T-80 tanks from the former USSR, and several older Chinese platforms - hardly becoming of a U.S. client state. With the United States having proven an unreliable partner, at times even supporting sanctions against Pakistan as a result of its nuclear program and failing to provide it with technology to match that provided by Russia to India, Pakistan’s pivot away from the U.S. could well be in the best interests of its defence sector.