it was rumoured that Ayub khan had an agreement with the PRC in 1965 regarding this issue. What stopped PRC from intervening in 1971 is the fact that Soviets massed their forces near the Sino-soviet border...is what Yahya Khan said before going to bed every night.
In this day and age of free-market capitalism where economies are linked with each other , wars like those of 65 and 71 cannot be waged.
After the indian parliament incident , indian armoured divisions positioned themselves near the Pakistani border. The US embassy instructed all of its citizens to leave India and the europeans followed suit. This caused a crisis in the indian economy overnight (investors got spooked) and forced them to the negotiating table.