Complex sentence: The Nguyễn fought on against both the Trịnh army and the Tây Sơn but their effort was in vain; by 1777 Saigon was captured and then nearly the entire Nguyễn Phúc family was killed, all except one nephew, Nguyễn Ánh who managed to flee to Siam.
Split into simpler sentences: The Nguyễn fought on against both the Trịnh army and the Tây Sơn, but their effort was in vain. By 1777 Saigon was captured and nearly the entire Nguyễn Phúc family was killed, all except one nephew, Nguyễn Ánh, who managed to flee to Siam.