Ghazwa-e-Hind refers to the prophecy of Prophet Muhammad (Pbuh) about a war which will be fought between Muslims against the unjust rulers of ‘Hind’.
There are many sayings and narrations that are attributed to Prophet Muhammad (PBUH) about this war among which many are weak but one hadith which is narrated by Thawbaan, the freed slave of the Messenger of Allah is considered Sahih by many scholars including Albaani.
There are many other ahadith with indicates other Hadith but scholars differ whether they are authentic or not including this narration by a companion of Prophet (PBUH).
Abu Hurayrah (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) promised us that we would conquer India, so if I am martyred I will be among the best of the martyrs, and if I return then I am Abu Hurayrah the freed (protected from Hellfire).
This is reported by Imam Ahmad in al-Musnad (12/28) and scholars in different books through different chains and narrators.
This indicates the importance of the war which most believe is yet to be fought. Many people believe that this will be war between Pakistan and India.
They claim Pakistan was created in the name of Islam and the people aspire to implement Islamic system in the country while on the opposite India represents Hindu nationalism where minorities are prosecuted which will eventually result in a full fledge clash.
Pakistan is also the only Muslim Country which is an atomic power with missiles technology that is considered among the best in the world. This increases the speculation that it may be the country which will conquer India.
While others believe that this war will be fought just before the coming of Imam Mehdi. There are many books especially in Urdu written by scholars about this prophecy.
During each tension between Pakistan and Indian people starts claiming that the Ghazwa has arrived, circulating the hadees and motivating people to get ready.
No one can exactly say which country will be the one who will initiative the war, but it is certain that the prophecy will became a reality some day!