of Vietnam, their most persistent and stubborn opponents were not the Vietnamese, but rather the Chinese mercenaries of the Black Flag Army commanded by Liu Yongfu, who been hired by the Emperor Tự Đức. In 1873, the Black Flags killed the French commander, Francis Garnier, attracting much attention in France. In 1883, Captain Henri Rivière, leading another French expedition into Vietnam was also killed by the Black Flags. When the French conquest of Vietnam was finally completed in 1885, one of the peace terms were the disbandment of the Black Flag Army. 20th century In the warlord period of China, many American and British mercenaries thrived such as Homer Lea, Philo Norton McGriffin, Morris "Two Gun" Cohen, and Francis Arthur "One Armed" Sutton. Easily the largest group of mercenaries in China were the Russian emigres who arrived after 1917 and who hired themselves out to various Chinese warlords in the 1920s. Unlike the Anglo-American mercenaries, the Russians had no home to return to nor were any foreign nations willing to accept them as refugees, causing them to have a grim, fatalistic outlook as they were trapped in what they regarded as a strange land that was as far from home as imaginable. One group of Russian mercenaries led by General Konstantin Petrovich Nechaev were dressed in the uniform of Imperial Russian Army and fought for General Zhang Zongchang, the "Dogmeat General" who ruled Shangdong province. Nechaev and his men were infamous for their ruthlessness, and on one occasion in 1926, rode three armored trains through the Chinese countryside, killing everybody they met. When the Chinese peasants tore up the rails to stop Nechaev's rampage, he and his men vented their fury by sacking in an especially brutal manner the nearest town. Another group of Russians wore Tartar hats and the traditional dark greycoats, and fought for Marshal Zhang Zuolin, the "Old Marshal" who ruled Manchuria. The Russian mercenaries had considerable effectiveness against the ill-trained armies of the Chinese warlords; one contemporary mentioned that how Marshal Zhang's Russians "went through the Chinese troops like a knife through butter". During the early stages of the Second Sino-Japanese War, a number of foreign pilots served in the Chinese Air Force, most famously in the 14th Squadron, a light bombardment unit often called the International Squadron, which was briefly active in February and March 1938. India 18th to 19th centuries In the medieval period,