Complex sentence: They built a fort there with forced labour recruited from the local Chinese population; their oversight was reportedly so severe and rations so short that 1,300 of the 1,500 Chinese enslaved died in the process of construction.
Split into simpler sentences: They built a fort there with forced labour recruited from the local Chinese population. Their oversight was reportedly so severe and rations so short that 1,300 of the 1,500 Chinese enslaved died in the process of construction.