Complex sentence: During the 1800s and the early 1900s, Nepal was under the reign of a highly centralized autocracy, the Rana Dynasty, which acted as a as monarchy; their policies resulted in the isolation of Nepal from the external world.
Split into simpler sentences: During the 1800s and the early 1900s, Nepal was under the reign of a highly centralized autocracy--the Rana Dynasty. The Rana Dynasty acted as a as monarchy; their policies resulted in the isolation of Nepal from the external world.