PACOM is short for Pacific Command.
ISI is short for Inter-Services Intelligence, the military intelligence arm of the Pakistan government. It would be equivalent to America's Defense Intelligence Agency, a division of the Department of Defense.
HAHO is short for High Altitude High Opening.
Ummah - Arabic word meaning "community", commonly used to refer to the collective community of Islamic people. The Quran mentions the ummah as being a group of people sharing the same common religious beliefs that are working together on a "divine plan of salvation". Groups like the Taliban and ISIS have perverted the meaning of the term ummah, they teach that a practicer of Islam is only considered to be part of the ummah if they are actively working to rid the world of infidels (non-believers).
Commander Shaw states that previous conflicts between India and Pakistan were the closest the world has been to nuclear war. It all started with the Indo-Pakistani War of 1971, which was a civil war in Pakistan that spilled out into India causing a full scale war between the two nations. The war was started when Pakistani forces carried out air strikes against Indian air bases, fearing that India would render aid to the rebel forces along the border, the conflict between the two nations only lasted a little over a week, but it made the Indian government begin to seek out ways to deter Pakistan from attacking them again. India began recruiting nuclear physicists and developing their own nuclear weapons program to obtain this goal, India managed to successfully create and test their first nuclear weapon in 1974. Pakistan had also been working on developing their own nuclear weapons since the 1971 conflict, but their efforts did not succeed as quickly. Pakistan was not able to create a functioning nuclear weapon until sometime in the early 1990's, unknown to the world they had created several functional warheads by 1998, which was the year India conducted its second nuclear weapons test. A few weeks after India's second nuclear weapons test Pakistan test detonated five nuclear devices on May 28, 1998, and then a sixth device a few days later on May 30th. Both nations placed their military's on high alert while the world at large feared the start of a nuclear conflict between the two nations.