Also, 50% population of Pak too.
Logistically and geographically, it's impossible for US and Chian to help BD in case of an Indo BD conflict. Nowhere, by land or sea or air.
Even if a help is sent, it's simply insane to hit Indian military in Bay of Bengal near India's East Coast and Indian military in Myanmar and it's own territory. There is a reason why India with even shit equipment could take over BD in 13 days during 1971 war.
BD's geograhic, military and economic disadvantage against India worse worse than condition of small post Soviet states against Russia. Preventing an Indian expedition of BD requires an expedition of India itself which is not practical for any country.
For vs BD part, Indian Armed forces will decimate their main command in days if not hours within starting of war. Problem will be guerilla warfare from local population (unless GoI chooses to do massacres which they won't).