Complex sentence: A recent Nepal Ethnographic Museum (2001) study postulated that Sherpas were not migrants who crossed the border of Tibet to Nepal, since the modern political entity of Nepal was not in existence then.
Split into simpler sentences: A recent Nepal Ethnographic Museum (2001) study postulated that Sherpas were not migrants who crossed the border of Tibet to Nepal. This is because the modern political entity of Nepal was not in existence then.