Complex sentence: Only a handful of Westerners are known to have traveled through the Wakhan Corridor since Marco Polo did it, in 1271, although there were sporadic European expeditions throughout the second half of the 19th century and the beginning of the 20th.
Split into simpler sentences: Only a handful of Westerners are known to have traveled through the Wakhan Corridor since Marco Polo did it, in 1271. There had been sporadic European expeditions throughout the second half of the 19th century and the beginning of the 20th.