Judaism failed because it sought proselytes instead of making converts.

Islam, the religion of Mohammed (in reality a Judaizing Christian sect) failed because it sought to make subjects rather than converts.

Its conquests over a variety of races were extensive, but not deep.

To-day it holds in its embrace at least four very distinct races,--the Arabs, a Semitic race, the Persians, an Indo-European race, the Negroes, and the Turks or Turanians.

But, correctly viewed, Islam is only a heretical Christian sect, and so all this must be credited to the interest of Christianity.