For long India said ISI was behind terrorist activities in India. USA was quiet. For some years Afghanistan said ISI was behind terrorist activities in Afghanistan. That included Indian Embassy. USA was quiet. When American Embassy was attacked USA spoke. Americans wanted Pakistan to take action against Haqqani group, veritable arm of ISI, or they will act on their own.
India should have acted on its own. USA has its interests. It will not act in favour of other countries unless it is for its own advantage or there is a lobby in USA that wants USA to act in favour of another country like Jewish lobby’s support for Israel. ISI got away with crimes against Indians and Afghans and became bold enough to attack Americans.
Pakistan’s army chief Ashfaq Parvez Kayani, who was once ISI chief, threatened retaliation if American soldiers entered Pakistan. He said Pakistan is not Iraq or Afghanistan and a nuclear power. It meant Pakistan will drop nuclear bombs on American soldiers. It halted American entry in Pakistan. Drone attacks are different matter.
It is unlikely ISI will stop its operations against Americans. Pakistan wants to control Afghanistan. Many Pakistani’s feel time is on their side, Americans will have to leave Afghanistan and after that Pakistan can dictate terms to Afghanistan. If USA stops assistance they can get it from Saudi Arabia. Saudi Arabia has emerged as a force. They have troops in Bahrain and have supported Saleh in Yemen. Saudi Arabia will support Pakistan against USA. China may sell arms to Pakistan but will not give assistance.
Some Pakistani politicians are not happy with ISI sponsoring terrorism but as long as army dominates Pakistan they cannot do much. When army domination ends Pakistan’s government can put an end to ISI activities. That does not seem possible in the near future.