Real Islam died with Prophet and his kins. Prophet died untimely despite he being healthiest person as per Hadiths. Then after a few years, his grandsons were killed. Ali, his son in law was also eliminated. Then rule of the killers of grandsons came. They propagated their own version of Islam through terror and blindness. Before Islam world in eastern side of Arab had never seen the madness that someone will rape and kill to promote a religious ideology!! It was easy for (new) Islam to conquer till India. India was mixed bag. While the terrorists tried hard, they could not be fully successful due to valor of natives here. That is why it could not move much beyond India. And in India, a new form of Islam came up that was completely different from that of Arab. Even today, despite great attempts by mullahs, Indian Islam and Arabic Islam are way apart.
In Europe, there was resistance from Christian. But because both cults were based on similar roots and ideology, except that Islam was younger, learned from Christian mistakes and hence much more ruthless. So it could still sneak out. Africa was open territory for both Christians and Muslims. So you see mixed impact.
Now Islam put lot of emphasis on breeding profusely. A translation of Quran even says: Women are like your production farms. I think it is 2.223.
While other religions see sin in sex, and respect right of woman to deny sex, Islam made it a religious order that no woman can refuse sex to husband. Also a liberal talaq system, polygamy, unlimited sex-slaves/ illegitimate relations made sure that there is no hindrance in having sex with women and hence breeding. So Islam spread by reproducing more than any other religious system. In India, Muslims were 7% during partition. Now they are at least 3–4 times. Many Islamic interpretaions gave further incentives to breed more children if you are in a country with significant non Muslim population. This is supposed to help establish Muslim rule in future.
Further more you breed, and more you breed children with Vitamin D deficiency in mother, and with marriage in close kins, medically it impacts the intelligence of children. So you create a population of less intelligent, who will be gullible and fanatic enough to continue violent and brutal ways. Ideal candidates for brainwashing.
Hence Islam spread fast. But this is not the Islam envisaged by Prophet Muhammad. It is Islam of Caliph Yazid gang that murdered prophet’s family.