Kill The Unbelievers
A year before he died Muhammad decided to raise the stakes with the revelation of al-Tawbah ("the Repentance"). He gave the tribes of Arabia 4 months grace but if by then they had not joined the Ummah and started to pay the zakat ("extortion tax") then Muslims must "slay the idolaters wherever you find them." At the time these "revelations" were passed on by Muhammad (the second last before he died) Muslims were still a minority in Arabia but a powerful one and various truces had been made with non-Muslim tribes. At this time all non-Muslims in Arabia except Christians and Jews were idolaters or pagans. According to these "revelations" God does not trust any non-Muslims, God says most non-Muslims are evil-doers and should be arrested, besieged, ambushed and killed wherever they can be found as soon as the truce ends. This is the "Holy" Quran. This is God speaking … or so Muslims believe.
Who else but Muhammad would declare an "immunity" which was really a threat of a war of conquest and absorption. These days, for political reasons, the concept of 'Jihad' is argued over but to Muhammad it appears he had decided that war against non-Muslims could be waged virtually at any time, without anything non-Muslims would consider a valid reason and in any place where non-Muslims could be found.
9.1: (This is a declaration of) immunity by Allah and His Apostle towards those of the idolaters with whom you made an agreement.
9.2: So go about in the land for four months and know that you cannot weaken Allah and that Allah will bring disgrace to the unbelievers.
9:3 A proclamation to the people from God and His apostle on the day of the greater pilgrimage: God and His apostle are under no obligation to the idolaters. If you repent, it shall be well with you; but if you give no heed, know that you shall not be immune from God's judgement. Proclaim a woeful punishment to the unbelievers,
9:4 except to those idolaters who have honoured their treaties with you in every detail and aided none against you. With these keep faith, until their treaties have run their term. God loves the righteous.
9:5 When the sacred months are over slay the idolaters wherever you find them. Arrest them, besiege them, and lie in ambush everywhere for them. If they repent and take to prayer and render the alms levy, allow them to go their way. God is forgiving and merciful.
9:6 If an idolater seeks asylum with you, give him protection so that he may hear the Word of God, and then convey him to safety. For the idolaters are ignorant men.
9:7 God and His apostle repose no trust in idolaters, save those with whom you have made treaties at the Sacred Mosque. So long as they keep faith with you, keep faith with them. God loves the righteous.
9:8 How can you trust them? If they prevail against you they will respect neither agreements nor ties of kindred. They flatter you with their tongues, but their hearts reject you. Most of them are evil doers. Quran (9:1-8)
Converting to Islam was a way of escaping death but could well be a difficult thing to manage when caught by a Muslim ambush, especially if this message hadn't reached you.
There were an awful lot of idolaters outside of Arabia who had no idea what Allah had in store for them. Most Muslim leaders very sensibly preferred to keep non-Muslims as dhimmis whose wealth could be raided or taxed rather than corpses though others more "Islamic idealistic" made serious efforts to kill all the polytheistic Hindus though they usually gave up when faced with the enormity of the task.