There had always been isolated persecution against non-Muslims since the beginning of Islam, but in the Arabian Peninsula in the mid 1700s, Wahabbism was born.  Followers of the Muhammad ibn Abd-al-Wahhab Najdi (say that three times fast) began practicing a strict interpretation of Islam and holy law, the Sharia.  This forbade the practice of any other religions, and this is still the law in Saudi Arabia today, though Wahabbis only make up a fraction of the royal family.

Najdi spread his brand of Islam to the royal family, the king, and throughout Saudi Arabia, and Christians at that time were heavily persecuted.