Complex sentence: He was the son of Prince Nguyen Phuc Huong Hoiou Cai, but because his uncle, the Tu Duc Emperor, had no children, he was adopted and made the Duke of Kien-Giang.
Split into simpler sentences: He was the son of Prince Nguyen Phuc Huong Hoiou Cai. Because he had no children his uncle, the Tu Duc Emperor, adopted him as one of his heirs and made him the Duke of Kien-Giang.