The immediate cause of the almost complete disappearance of organised Buddhism from northern India after the 12th century was without doubt its persecution during the Islamic invasions between the years 1001 and 1199. The first Muslims to invade were Arabs under the leadership of Muhammad bin Kasim, who conquered Sindh in about 712, systematically destroying its Buddhist institutions, persecuting the religion’s followers and gradually converting the local populace to Islam. The next Muslim invaders were the Yamini Turks led by Sultan Mahmud, who between 1001 and 1027 launched at least 17 military incursions into India from Afghanistan with devastating consequences endured particularly by the Buddhist community.
The next large Muslim invasion took place in 1175 under Muhammad Ghuri, who made it as far as Thanesar just north of Delhi before being blocked by the united armies of the Hindus in 1191. He returned a year later and completely overwhelmed the Indians, sweeping away resistance to his eastward march. At this point Qutb-ud-din Aibak, a former slave from Turkestan, was appointed commander of the avaricious hordes, who in 1193 succeeded in capturing Delhi. It took only four more years under the leadership of the notorious Muhammad Khilji to sweep across Uttar Pradesh and conquer the whole of Bihar in the northeast. Muslim historians proudly record that the inhabitants of this area were mostly bare-shaven Brahmins who were ruthlessly put to the sword. There can be little doubt that these victims of Muslim hegemony were mostly peace-abiding Buddhist monks whose monasteries were systematically defiled, plundered and subsequently destroyed. Meanwhile, Muhammad Khilji drove further eastward and conquered Bengal in 1199–1200, without meeting any serious resistance.
The complete subjugation of northeastern India by the Muslims in the late 12th century resulted in the swift and almost complete extinction of organised monastic Buddhist activities, which never recovered.
The eastward drive of the Muslims came to an end in Bengal in the years 1199-1200 as a result of Burmese resistance.
Without the Burmese bulwark, Muslim conquerors would have carried their jihad further east and likely wiped out Buddhism in Myanmar, Thailand and surrounding countries.
Thus the so-called Rohingya crisis marks the point at which the 800-year eastward expansion of Islam was successfully checked.