He returned home, and began to attempt the conversion of proselytes to this belief; but his progress was slow, and the opposition he provoked bitter and deadly. He was in his fifty-third year when the crisis of his career arrived, and he had to fly, at the imminent peril of his life, from Mecca to Medina. This is regarded by the disciples of Islam as the first open promulgation of their faith. At Medina he found himself at the head of an armed force, with which he resolved to enter on his mission of converting the world. At the same time he determined that the instrument by which this was to be effected was the sword. The attempt seemed a wild one. Yet we must remark that the condition of the world at that period was unusually favourable to it. There existed then but two powerful sovereignties—the Eastern Empire, governed by Heraclius, and the Persian kingdom of Chosroes and afterwards of Yezdegird. The two last named were men of very ordinary capacity; and either indolence or the pressure of external circumstances kept Heraclius inactive. Nor could they command the services of any great soldier, such as Aetius, or Narses, or Belisarius, whose military genius might avail in driving back the invasion of barbarous and fanatic hordes. They were also greatly weakened by long and desolating wars. But, however propitious the occasion may have been, it is obvious that Mahomet, whatever might be his ultimate views, could not then attempt hostile measures against them. Necessarily his first task must be to reduce to obedience the inhabitants of Arabia itself; and the most formidable of these were the various Jewish communities, with which the land was at that time overspread.