China hasn't traditionally needed land. China has occupied a landmass greater than all of Europe combined for almost two thousand years. The population has always been large, but only in relatively modern times has the land been pressed to its maximum carrying capacity. Cyclical disasters; earthquakes, typhoons, floods, epidemic disease and famine generally kept the population below critical mass. The greater portion of Chinese have always been rural peasants working small plots of ground. Rice, a major staple, is very labor intensive and so large families were always desirable. Infant mortality was high and sons were valued as the primary Social Security system for a parent's old age. Females tended to be regarded as less valuable additions to the family's survival. Until modern times the whole system maintained a haphazard balance, but modern technology and medicine have greatly reduced infant mortality, and increased longevity. The general health of the population has improved. The uninteded result has been a population explosion that is threatening to far outstrip the agricultural capacity of the land as it is being used.
The reason sons are valued as social security is because grandparents and parents used to live together with the oldest son's family. There was no government pension available.
I'm not sure about Thailand, but I know that China attempted to conquer Korea many times. The Sui Dynasty of China sent nearly a million troops in an effort to conquer the Korean kingdom Goguryeo but failed (a major factor in the Sui dynasty's downfall). The Tang dynasty attempted several times and failed until they were aided by another Korean kingdom by the name of Silla. United, these two defeated Goguryeo and split its territory (Manchurian territories were given to the Tang and the territory on the Korean peninsula was given to Silla). So basically, China tried many times but were never successful.
@cello,
Korea uses its own characters. an alphabet called hangeul, which was invented in 1443 AD under the reign of Sejong Daewang. Before it used hanja, which was basically a Korean usuage of Chinese characters. In South Korea, Hangul is occasionally augmented by hanja; whereas in North Korea, hanja are virtually nonexistent.
