The first general of the empire was Khalid ibn Walid. During his campaign against the Persian Empire("Iraq 633 - 634") and Byzantine Empire ("Syria 634 - 638") Khalid developed brilliant tactics. The Caliph Abu Bakr's way was to give his generals their mission, the geographical area in which that mission would be carried out, and the resources that, could be made available for that purpose. He would then leave it to his generals to accomplish their mission in whatever manner they chose, on the other hand Caliph Umar in later part of his Caliphate used to direct his generals as to where they would stay and when to move to the next target and who will be commanding the left and right wing of the army in the particular battle, this made the phase of conquest comparatively slower but provided well organized campaigns. Caliph Uthman used the same method as of Abu Bakr, he would give missions to his generals and then leave it to them how they accomplish it. Caliph Ali also followed the same method.