Mohammed was succeeded in his power by rulers called his _Caliphs_, or
Successors, the first of whom was his father-in-law, Abu-beker. They
were at once spiritual and temporal rulers. The proselyting spirit of
Mohammed had been communicated to his successors, and they began a long
series of invasions, wars, and conquests. They everywhere gave men the
choice of three things,--Koran, tribute, or sword. By these means the
religion of Mohammed was spread over a large part of Asia and Africa,
and made its way into Europe also.