And so it came to pass that all the Bedouin tribes
were in the end converted outwardly, but not from inward
conviction.[39]

[Sidenote: The Arabs thus reclaimed were, at the first, sullen.]
The temper of the tribes thus reclaimed by force of arms was at the
first strained and sullen. But the scene soon changed. Suddenly the
whole peninsula was shaken, and the people, seized with a burning zeal,
issued forth to plant the new faith in other lands. It happened on this
wise:

[Sidenote: Roused by war-cry, they issue from the peninsula, A.D. 634,
_et. seq._
The opposing forces.
Arab enthusiasm.]
The columns sent from Medina to reduce the rebellious tribes to the
north-west on the Gulf of Ayla, and to the north-east on the Persian
Gulf, came at once into collision with the Christian Bedouins of Syria
on the one hand and with those of Mesopotamia on the other. These again
were immediately supported by the neighboring forces of the Roman and
Persian empires, whose vassals respectively they were. And so, before
many months, Abu Bekr found his generals opposed by great and imposing
armies on either side. He was, in fact, waging mortal combat at one and
the same moment with the Kaiser and the Chosroes, the Byzantine emperor
and the great king of Persia. The risk was imminent, and an appeal went
forth for help to meet the danger. The battle-cry resounded from one end
of Arabia to the other, and electrified the land. Levy after levy, _en
masse_, started up at the call from every quarter of the peninsula, and
the Bedouin tribes, as bees from their hive, streamed forth in swarms,
animated by the prospect of conquest, plunder, and captive damsels, or,
if slain in battle, by the still more coveted prize of the "martyr" in
the material paradise of Mohammed. With a military ardor and new-born
zeal in which carnal and spiritual aspirations were strangely blended,
the Arabs rushed forth to the field, like the war-horse of Job, "that
smelleth the battle afar off, the thunder of the captains and the
shouting." Sullen constraint was in a moment transformed into an
absolute devotion and fiery resolve to spread the faith. The Arab
warrior became the missionary of Islam.

[Sidenote: Arabs, a military body, subsidized and mobilized by Omar.]
It was now the care of Omar, the second caliph or ruler of the new-born
empire, to establish a system whereby the spirit militant, called into
existence with such force and fervor, might be rend