Complex sentence: He lost his power over Persia in a battle against the Mongols in the Alborz Mountains and fled to the Caucasus and captured Azerbaijan in 1225, setting up his capital at Tabriz.
Split into simpler sentences: He lost his power over Persia in a battle against the Mongols in the Alborz Mountains. Escaping to the Caucasus, he captured Azerbaijan in 1225, setting up his capital at Tabriz.