At the time of the advent of Islam, there were two very great empires in the world —the Christian Roman Empire and the Zoroastrian Persian Empire. There were constant clashes between these two. In the year 603 A.D., Iran (Persia) attacked the Roman Empire, taking advantage of certain weaknesses in the latter. The Romans suffered defeat after defeat, so much so that by the year 616 A.D., a large part of the Roman Empire, including Jerusalem, had been captured by the Iranians. The Prophet received the prophethood in the year 610 A.D. and he started upon the task of explaining the Oneness of God in Makkah. This was the period of the struggle between monotheism and polytheism in that city. The polytheists of Makkah, taking their cue from the events on the border, told the Muslims that their polytheist brothers, the fire-worshipping Zoroastrians, had defeated the possessors of the Book and brothers of the Muslims (namely, the Christians) and that in the same manner they (the polytheists of Makkah) would finally overwhelm the Muslims. At that time, completely against the prevailing trend, the Quran predicted that within ten years, the Romans would regain supremacy over the Iranians. Roman historians say that immediately thereafter the vanquished King of the Romans, Heraclius, started undergoing a mysterious change, so much so that in the year 623 A.D., he led a retaliatory attack on Iran. In the year 624 A.D., he achieved a decisive victory over Iran. By the year 627 A.D., he had recovered all his occupied territories from the Iranians. Thus it was proved that the Quran was a revelation from God, as nobody else except God could have made such statements about the future so accurately. Moreover, these events indicate that victory or defeat are directly in the hands of God. It is according to His decision who gains and who loses power. The downfall of a nation and the rise of another nation, to all appearances seem to be ordinary, normal, worldly events, but appearances have an inner aspect to it. Every event is caused by a number of angels of God, though they are not visible to ordinary human eyes. Similarly, there is an invisible aspect of the present, outward world and it is the world of the Hereafter.