Muhammad: The Failed Prophet and the Treacherous Warlord
It is impossible to understand Islam without knowing that Muhammad had 2 completely different sections in his life. In his first life he was a poor orphan born in 570AD who got ahead by marrying his much older employer, the wealthy widow Khadija. When he was 40 he began having "revelations" and began preaching a monotheistic religion in Mecca which was the trading, religious and pilgrimage centre of Arabia. Meccan society was profusely and profitably polytheistic and Muhammad's uncompromising monotheism and threatening tirades and prophecies did not endear himself to the wider community. In fact, he was the local butt of jokes and ridicule and his egoism and megalomania were not matched by charisma and brilliance and his career as a poet and prophet was a dismal failure. Over a 12 year period of public proselytisation he converted only a few hundred followers. Some of his "revelations" in this period demanded what we would now call social justice and toleration as we might expect from a powerless leader of a small cult though even in this time they were a minor part of his message. The conventional wisdom is that Muhammad was persecuted by an elite who were afraid his monotheistic teachings might lessen the profits flowing from Mecca's position as the centre of Arabian polytheism but this seems far-fetched in light of his failure to attract converts.
In 622AD Muhammad and his followers left Mecca and emigrated to Yathrib (renamed Medina) a wealthy town dominated by 3 tribes of Jews who owned date plantations and were artisans. Muhammad now begun the second part of his life as an aspiring political leader and warlord and in this he was spectacularly successful.
7th century Mecca was a highly tolerant and religiously pluralistic society but only Muslims were allowed into Mecca once Muhammad got control. A non-Muslim saint wouldn't be allowed into Mecca but a Muslim mass murderer would have no problems. As the Quran says:
"Oh you who believe! Truly the idolaters are unclean; so let them not, after this year, approach the Sacred Mosque …" - Quran (9:28)
From the very first revelation, Allah threatened anyone who believe in him with hell.
Hast thou seen if he denieth (Allah's guidance) and is froward? Is he then unaware that Allah seeth? Nay, but if he cease not We will seize him by the forelock - The lying, sinful forelock - Then let him call upon his henchmen! We will call the guards of hell. - Quran (96:13)