Complex sentence: When France had finished its conquest of Vietnam in 1885, only southern Vietnam was made a direct colony under the name of Cochinchina, while the northern and central regions were designated as protectorates as Tonkin and Annam.
Split into simpler sentences: When France had finished its conquest of Vietnam in 1885, only southern Vietnam was made a direct colony under the name of Cochinchina. The northern and central regions were designated as protectorates as Tonkin and Annam.