After the government of Song China failed to pay the officials in some provinces in 1306 (3003, Yang Fire Horse in the Chinese calendar), the unrest grew. People more and more agreed that the emperor had lost the Mandate of Heaven. In this year, the rebellions started with Szechuan seceding from the empire, becoming an independent kingdom. 1309 (3006, Yin Earth Chicken), all of South China was in unrest. The emperor was killed in the chaos. Jin China also used the opportunity to plunder and annex parts of the Yangtse area. Many wars and revolts shook up South China for some time.
In 1330 (3027, Yang Metal Horse), after the dust has settled in China, the so-called Four Kingdoms had formed: Szechuan, one kingdom of the Coastal areas, one kingdom along the Yangtse and one kingdom in the inner parts, named after the city of Hong.
1344 (3041, Yang Wood Monkey), the Black Death hit Hong.
Reunification of China
In 1355/56 (3052, Yin Wood Sheep / 3053, Yang Fire Monkey), the first Hong emperor (then, still considered one king among many) stroke against the Yangtse kingdom, divided it in two and then made peace.
1357-60 (3054, Yin Fire Chicken / 3057, Yang Metal Rat), he made war against the South Chinese coast kingdom, conquered Wengzhou, thereby dividing his strongest two enemies.
Then, in 1358 (3055, Yang Earth Dog) the Jin empire demanded from him to pay tribute. He gave in, for the moment.
The year 1367 (3064, Yin Fire Sheep) saw a Border war between Hong and Pagan; the first one was victorious, Pagan had to give the conquered Chinese lands back and pay a tribute - the first one Hong China received.
During 1371-75 (3068, Yin Metal Pig / 3072, Yin Wood Rabbit), the old Hong emperor made war against the South Chinese coast kingdom again. At first, the war was lead by land, but since the army of Hong wasn't making progress fast enough, Hong China started to build a fleet of cannon-armed junks which bombarded Canton and other cities. South China was united again after this war.
Under his son, in 1381 (3078, Yin Metal Chicken) Hong China stopped paying tribute to the Jin. A new war started. It proved now, however, that Jin China, although it seemed to be strong on the outside, depended too much on mercenaries.
1387 (3084, Yin Fire Rabbit), the War between Hong and Jin started again. In 1390, Goryeo entered the war on Hong China's side against Jin.
1392 (3089, Yang Water Monkey), the Hong conquered Beijing, the Jin empire was destroyed, the surviving Jin leaders decapitated. The emperor decided that the Great Wall was to be repaired and extended.
Expansion of influence
Even before the unification of China was complete, Hong China had projected its power over the traditional borders. With the new-built fleet, the emperor made the first campaign against the Nipponese pirates around Tungning (OTL Taiwan) in 1385 (3082, Yin Wood Ox). In the same year, Hong China and Annam made Champa a tributary, as it had been under earlier dynasties.
In 1403 (3100, Yin Water Sheep), China established a trade post at Aparri, Luzon, OTL Philippines, which would become important later.
The Treasure Ships
1400-02 (3097, Yang Metal Dragon / 3099, Yang Water Horse): First voyage of Chinese Treasure Ships. They travelled to Pasai (Sumatra), Melaka (OTL Malacca), Ayutthaya, Khmer, Pagan, to arrive in Calicut.
1404-06 (3101, Yang Wood Monkey / 3103, Yang Fire Dog): Second voyage of Chinese Treasure Ships. They travelled to Calicut again, and also visited Sri Lanka, which king accepted the Hong as supreme rulers.
1407-09 (3104, Yin Fire Pig / 3106, Yin Earth Ox): Third voyage of Chinese Treasure Ships. This time they went east, to Brunei, Majapahit, and even discovered the north coast of Antipodia (OTL Australia) (although they weren't interested in the latter).
1416-19 (3113, Yang Fire Monkey / 3116, Yin Earth Pig): The great voyage: Chinese Treasure Ships went to Hormuz, visited Persia and opened diplomatic relations, and a part of them sails down the African coast to Mozambique. Following them, Chinese merchants opened new trade connections. Although under the Hong trade was still somewhat despised, they tended to accept it as a necessary evil - especially since the revenue wasn't something to sneer upon.
1408 (3105, Yang Earth Rat): The ruler of Melaka marries a Chinese noblewoman, starts paying a small tribute to China. This is one of many signs of the cultural changes brought to SE Asia by the Chinese.
1419: Grand Canal between South and North China renewed.
1420s: Civil War in Majapahit. China intervenes here, too. By playing out the empires of Melaka and Majapahit against each other, they put sure that neither gains the upper hand.
1422 (3119, Yang Water Tiger): Chiang Mai (Northern Thailand) pays tribute to Hong.
1425/26 (3122, Yin Wood Snake / 3123, Yang Fire Horse): Annamese uprising defeated.
1430s: Inner conflicts in Pagan split the country in two halfs. One of them, the Pegu dynasty (from the city with the same name), asks Hong China for help, gaining control of the rest of OTL Burma. China's sphere of influence now borders India.
1446 (3143, Yang Wood Tiger): Thai conquer Angkor Wat, threaten to destroy the Khmer empire. Khmer appeal to the Hong Emperor to help them. The emperor agrees, threatens Thai; when the latter refuse, war starts in 1447 (3144, Yin Wood Rabbit).
1450 (3147, Yang Metal Horse): Thai are defeated, have to pay tribute to China.
1451 (3148, Yin Metal Sheep): Tibet joins the Chinese sphere of influence.
1452-56 (3149, Yang Water Monkey / 3153, Yang Fire Rat): A Chinese treasure fleet sails up the Red Sea, sends a delegation to Egypt. On their return, they also spread tales about the Christian countries.
1453 (3150, Yin Water Chicken): Assam start paying tribute to the Hong.
1457 (3154, Yin Fire Ox): A crisis at the court of the ninth Hong emperor is solved in a pleasing way.
1463 (3160, Yin Water Sheep): Arakan (Assam's neighbor) also becomes part of the Chinese sphere of influence.
1464 (3161, Yang Wood Monkey): Arabs in the city of Taiz, Hejaz, assault the crew of a Chinese ship when they went on land. Although the authorities don't want to anger off the strong Chinese fleet, things become complicated when the assaulters can't be caught, but demand ransom for the crew. The Chinese pay the money, but after the captured crew is returned, they demand from the Seljuk authorities that they punish the criminals, or at the very least return the money. After a demonstration of their cannons' power, the sherif gives in. Some henchmen are actually captured, but their leader stays hidden. The Chinese leave, but many Arabs aren't happy about his humiliation.
1466 (3163, Yang Fire Dog): News of the assault spread to the court, who decided to send another fleet of cannon-stocked ships, which reaches Arabia now. The Chinese approach the Omanis (with whom they have more and better contacts), win them as allies against the Hejaz Arabs.
1474 (3171, Yang Wood Horse): Thai ask Hong emperor to solve a struggle for succession, which he does. This is the precedent for extending Chinese influence in Ayutthaya.
1483 (3180, Yin Water Rabbit): War between the Rum-Seljuks and the Hong breaks out, which distracts the Seljuks somewhat from defeating Hungary. Battles in the Red Sea, Omanis make incursions into Hejaz.
Late 1480s: Another uprising against Chinese by Vietnamese, which is suppressed. Annam practically becomes a Chinese province.
1487 (3184, Yin Fire Sheep): Seljuk-Hong war ends with a peace. The Seljuks will send a regular tribute/gift to the Hong emperor, who'll return the favor. Since this is a generous peace, the Seljuks accept it. Arabs start trading with China, bringing glassworks, plants from the Middle East, like coffee, qat and hashish, to China.
1492 (3189, Yang Water Rat): Sultan of Bengal pays tribute to Hong.
~1500: Russian merchants make first contact with Chinese traders.