e at Rome was
rent asunder by the inrush of barbarians; but upon its ruins was
erected the great Catholic Church of the Papacy, which preserved in
the ecclesiastical domain the autocratic imperial tradition. The
primacy of the Roman Church, according to Harnack, is essentially the
transference to her of Rome's central position in the religions of the
heathen world; the Church united the western races, disunited
politically, under the common denomination of Christianity. Yet
Christianity had not long established itself throughout all the lands,
in Europe and Asia, which had once been under the Roman sovereignty,
when the violent irruptions of Islam upset not only the temporal but
also the spiritual dominion throughout Western Asia, and along the
southern shores of the Mediterranean. The Eastern empire at
Constantinople had been weakened by bitter theological dissensions and
heresies among the Christians; the votaries of the new, simple,
unswerving faith of Mohammed were ardent and unanimous. In Egypt and
Syria the Mohammedans were speedily victorious; the Latin Church and
even the Latin language were swept out of North Africa. In Persia the
Sassanian dynasty was overthrown, and although there was no immediate
and total conversion of the people, Mohammedanism gradually superseded
the ancient Zoroastrian cultus as the religion of the Persian State.
It was not long before the armies of Islam had triumphed from the
Atlantic coast to the Jaxartes river in Central Asia; and conversion
followed, speedily or slowly, as the direct result of conquest.
Moreover, the Mohammedans invaded Europe. In the south-west they
subdued almost all Spain; and in the south-east they destroyed, some
centuries later, the Greek empire, though not the Greek Church, and
consolidated a mighty rulership at Constantinople.

With this prolonged conflict between Islam and Christianity along the
borderlands of Europe and Asia began the era of those religious wars
that have darkened the history of the Western nations, and have
perpetuated the inveterate antipathy between Asiatic and European
races, which the spread of Christianity into both continents had
softened and might have healed. In the end Christianity has fixed
itself permanently in Europe, while Islam is strongly established
throughout half Asia. But the sharp collision between the two faiths,
the clash of armies bearing the cross and the crescent, generated
fierce fanaticism on both sides. The Cr