During the Ming Dynasty, tea-horse policy was greatly developed; tea-horse trade offices were set up in all districts, and the exchange rate of tea and horses was also stipulated: one best-quality horse for 60 kg of tea; one mid-quality for 35 kg of tea and one foal for 25 kg of tea. Private trade was forbidden. Gold plates were granted to the heads in Tibet and other areas inhabited by people " at the top, "For Official Errand" on the left and "anyone committing an offence should be beheaded" on the right. The Ming court also actively tackled ffences in the tea-horse trade. It was stipulated that "anyone who exports tea privately is guilty of a crime worthy of death." But it was still difficult to prevent some businessmen and officials trying to profit in this way. Zhu Yuanzhang's son-in-law Ouyang Lun, for example, did so. When his activities were disclosed, Zhu Yuanzhang placed righteousness above family loyalty and killed this emperor's son-in-law. Role in Anti-Japanese WarAccording to some records, all professional horse caravans before liberation had a rigorous organization including three grades of No.1 Guotou, No.2 Guotou and Guanshi. Daguotou was head of the whole caravan and was brave and resourceful, familiar with business information, folk customs and road posts, and could manage household and financial affairs such as managing housekeepers, beasts and property. The size of the horse caravans differed according to the number of beasts. Five beasts constituted a bundle, five bundles constituted a small caravan with a small Guotou in charge. One caravan had scores of beasts, and could have hundreds or even thousands. There was one driver to four mules and horses. (See Shen Xu: "The Tea-Horse Trade Route-a history once disappeared").As the Tea-Horse Trade Route was long, dangerous and rough, people making the difficult journey on the ancient roads year in and year out showed fortitude and an adventurous spirit. But in their hearts was hidden some bitterness that could not be exposed to others. There was a saying in horse caravan business that "the money earned on this route can be enjoyed by nobody but parents." During the period of World War II, when Japanese imperialists invaded China, the horse caravans and heads of tea houses on the Tea-Horse Trade Route made a great contribution. After Burma (Myanmar) was occupied by the enemy, in order to prevent the invasion of the Japanese army to the east of the Nujiang River, the Chinese army bombed Huitong Bridge to cut off the unique international road in the southwest area, the Yunnan-Myanmar Highway, and the Tea-Horse Trade Route took on new importance. The materials for the battle supported by overseas Chinese and allied forces including arms and ammunition were brought from India continuously to China by horse caravans. Members of the horse caravans came from the Tibetan, Naxi, Bai and Han ethnic groups. They were not only partners in business but also comrades-in-arms in the Anti-Japanese War. Many more horse drivers joined the army directly and became soldiers, being familiar with the terrain and roads, and able to shoot and fight with great bravery. At that time there was a popular song, "Horse bells jingle all the way, and horse Guotou are full of mettle. Don't do business this year and carry guns to fight for the country."