Complex sentence: In the early eighteenth century Mohammerah (which means "reddened" in Arabic) became a Sheikhdom in Arabistan region it flourished until 1925 when Reza Shah conquerd this independent city and changed its original Arabic name into a Persian name (Khorramshahr).
Split into simpler sentences: In the early eighteenth century Mohammerah (which means "reddened" in Arabic) became a Sheikhdom. In 1925, Reza Shah re-conquered the city and changed its Arabic name into a Persian name (Khorramshahr).