Complex sentence: He instructed his followers to create a secret route from Ha Tinh through Laos into north-eastern Siam; one such route from Mount Vu Quang was believed to have been created in around 1888.
Split into simpler sentences: He instructed his followers to create a secret route from Ha Tinh through Laos into north-eastern Siam. One such route from Mount Vu Quang was believed to have been created in around 1888.