Complex sentence: He is best known for his defiance of the emperor in leading a guerrilla army in southern Vietnam against the French invasion, refusing to recognise the 1862 Treaty of Saigon that ceded Vietnamese territory to France.
Split into simpler sentences: He is best known for leading a guerrilla army in southern Vietnam against the French invasion in defiance of the emperor. He refused to recognise the 1862 Treaty of Saigon that ceded Vietnamese territory to France.