world. Perhaps the main cause is the immense population of China, with
an almost complete identity of culture throughout. In the middle of the
eighth century, the population of China is estimated at over 50
millions, though ten years later, as a result of devastating wars, it is
said to have sunk to about 17 millions.[13] A census has been taken at
various times in Chinese history, but usually a census of houses, not of
individuals. From the number of houses the population is computed by a
more or less doubtful calculation. It is probable, also, that different
methods were adopted on different occasions, and that comparisons
between different enumerations are therefore rather unsafe. Putnam
Weale[14] says:--

The first census taken by the Manchus in 1651, after the
restoration of order, returned China's population at 55 million
persons, which is less than the number given in the first census
of the Han dynasty, A.D. 1, and about the same as when Kublai
Khan established the Mongal dynasty in 1295. (This is presumably
a misprint, as Kublai died in 1294.) Thus we are faced by the
amazing fact that, from the beginning of the Christian era, the
toll of life taken by internecine and frontier wars in China was
so great that in spite of all territorial expansion the
population for upwards of sixteen centuries remained more or less
stationary. There is in all history no similar record. Now,
however, came a vast change. Thus three years after the death of
the celebrated Manchu Emperor Kang Hsi, in 1720, the population
had risen to 125 millions. At the beginning of the reign of the
no less illustrious Ch'ien Lung (1743) it was returned at 145
millions; towards the end of his reign, in 1783, it had doubled,
and was given as 283 millions. In the reign of Chia Ch'ing (1812)
it had risen to 360 millions; before the Taiping rebellion (1842)