dates back to the origins of Islam in that it is a function of the Prophet's lack of providing for a successor which caused the difficulty in the first place. And the effects of this was that for centuries after Muhammed's death, the subject of who was to follow him because the root of much evil, strife, schisms, and bloodshed.
From its earliest history, Islam was a religion with a zeal for expansion. Before his death, Muhammed ahd brought under his influencemost of the inhabitants of Arabia, with the exceptions of the Jews , a few Christians and Magians, whom he permitted to remain in thier own faith as long as they recognized his political rule by the payment of a poll-tax. However, he excluded them and other nonbelievers from the communal life by forbidding them access to Mecca, a prohibition which continues in force to this day.
Upon the prophet's death, widespread fighting and revolts broke out among the various tribes that had come under Muhammed;s banner, The first Caliph, Abu Bakr, who was Muhammed's father-in-law succeeded in reuniting Islam, though after much fighting and cloodshed. In 633, Khalid ibn `Arabi conquered Persia and shortly after, Syria and Palestine. Jerusalem was taken by the end if 636. By the year 641, the whole of western Iraq and Mesopotamia as far as Mosul was in Muslim hands, and there wwere forays in to Armenia. The first movement in to Asia Minor occurred in about 640-641 and by 652 the Arabs were in sight of Constantinople. But it was not until 717 that a serious attack on this vital city was made. But they were eventually driven out of Asia Minor.
However, in the ensuing decades, much progress was made in conquering the northern portion of Africa. The result was that in 711, the Muslims crossed over into the Iberian Peninsuka and, with the exception of the Cantabrian and Pyrenean highlands, overran the peninsula. They remained in Iberia until the fall of Granada in 1492. It...