Senachian Jihad
Military action
Newly established religion of Hezri begins to expand, quickly conquering and converting most of Senachian Peninsula.
Despite Hezri's ultimate death (or ascension to Heavens, as there are many versions depending on who is talking) his religion spread forward.
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Soon forces of newly established Caliphate began its expansion, quickly overwhelming scattered tribes and small (and insignificant) countries. Most of their population is soon converted.