Complex sentence: During his tenure as I Corps Commander, the Buddhist Uprising started in the region because his predecessor Nguyen Chanh Thi was very popular and was dismissed by military rival Nguyen Cao Ky.
Split into simpler sentences: During his tenure as I Corps Commander, the Buddhist Uprising started in his region. This was because his predecessor Nguyen Chanh Thi was very popular and was dismissed by military rival Nguyen Cao Ky.