Within 77 years of death of its prophet in AD 632. Palestine and Syria fell to ISLAM after a six months campaign in AD 636-637. Next came the turn of the Sassanid empire of Persia which included Iraq, Iran, and Khorasan. The Persians were defeated decisively in AD 637, and their entire empire was overrun in the next few years. The Turkish speaking territories of Inner Mongolia, Bukhara, Tashkand, and Samarkand, etc. were annexed by AD 650. Meanwhile, in the west, Egypt had fallen in AD 640-641. The Arab armies marched over North Africa till they reached the Atlantic and crossed over into Spain in AD 709.
These were not mere territorial conquests.. Syrians, Persians, Berbers, Turks and others - all were rapidly Islamised and their language and culture Arabicised. All this was in accordance of the passage of the Quran which had inspired the Arabs to decimate and denationalise those who were defeated by them: Fight and slay the pagans wherever you find them, and seize them, beleaguer them and lie in wait for them in every stratagem till they repeat and establish regular prayers and practise regular charity.
The same Islamic armies, however, had to struggle for 69 long years to make their first effective breach in the borders of India. In the next three centuries, they pushed forward in several provinces of Northern and Western India. But at the end of it all, India was far from being conquered militarily or assimilated culturally. The Arab invasion of India ended in a more or less total failure.