These stupendous conquests which laid the foundations of the Arab empire, were certainly not the outcome of a holy war, waged for the propagation of Islam, but they were followed by such a vast defection from the Christian faith that this result has often been supposed to have been their aim. Thus the sword came to be looked upon by Christian historians as the instrument of Muslim propaganda, and in the light of the success attributed to it the evidences of the genuine missionary activity of Islam were obscured. But the spirit which animated the invading hosts of Arabs who poured over the confines of the Byzantine and Persian empires, was no proselytising zeal for the conversion of souls. On the contrary, religious interests appear to have entered but little into the consciousness of the protagonists of the Arab armies. [46] This expansion of the Arab race is more rightly envisaged as the migration of a vigorous and energetic people driven by hunger and want, to leave their inhospitable deserts and overrun the richer lands of their more fortunate neighbours. [47] Still the unifying principle of the movement was the theocracy established in Medina, and the organisation of the new state proceeded from the devoted companions of Muḥammad, the faithful depositaries of his teaching, whose moral weight and enthusiasm kept Islam alive as the official religion, despite the indifference of those Arabs who gave to it a mere nominal adherence. [48] It is not, therefore, in the annals of the conquering armies that we must look for the reasons which lead to the so rapid spread of the Muslim faith, but rather in the conditions prevailing among the conquered peoples. The national character of this ethnic movement of migration naturally attracted to the invading Arab hosts the outlying representatives of the Arab race through whom the path of the conquering armies lay. Accordingly it is not surprising to find that many of the Christian Bedouins were swept into the rushing tide of this great movement and that Arab tribes, who for centuries had professed the Christian religion, now abandoned it to embrace the Muslim faith. Among these was the tribe of the Banū Ghassān, who held sway over the desert east of Palestine and southern Syria, of whom it was said that they were “Lords in the days of the ignorance and stars in Islam.” [49] After the battle of Qādisiyyah (A.H. 14) in which the Persian army under Rustam had been utterly discomfited, many Christians belonging to the Bedouin tribes on both sides of the Euphrates came to the Muslim general and said: “The tribes that at the first embraced Islam were wiser than we. Now that Rustam hath been slain, we will accept the new belief.” [50] Similarly, after the conquest of northern Syria, most of the Bedouin tribes, after hesitating a little, joined themselves to the followers of the Prophet. [51]