During the hundred years, the population of the R.O.C. changed dramatically from growth to decrease. In the early years after the R.O.C. was established, the country’s population stably grew as other countries in this period. After WWII, as well as other countries, the R.O.C. also experienced baby boom, which led to rapid increase in population. Sequentially, as the R.O.C. government actively promoted Family Planning, the growth of population slowed down. Afterwards, the R.O.C. has gone through a series of social changes that influenced the country’s population changes, and by around 2021, the R.O.C. is predicted to face negative growth in population. There are two factors affecting on the changes in population, natural increase and social increase. Natural increase refers to subtracting the number of death from the number of birth, which would led to increase or decrease in population; on the other hand, social increase refers to people immigrate from one place to another, and the number of migration coming from the counterbalance of the number of moving in and moving out would also lead to positive or negative growth in population. During the hundred years, there were few large-scale migrations, so the influence of social increase was rather limited. From 1923 to 1929, it is estimated that 3,500,000 people moved to nearby countries and that nearly 500,000 people moved back to China. Apart from that, in 1946, about 530,000 Japanese were sent back to Japan, and around 1949, almost 1,000,000 people moved to Taiwan with the nationalist government. Comparing to the number of hundreds- million population, the number of immigration had few influence on the number of total population. As a result, the major factor that caused changes in population was natural increase in the hundred years.

     According to the changes of death rate and birth rate, the change of population in the past of all the countries can be divided into four phases, in theory: 1. Before a society’s modernization, birth rate and death rate are both high in the society, and the number of population changes little. 2. In the early stage of modernization of the society, birth rate is still high, but death rate gradually decreases. Therefore, natural increase grows in number. 3. The advanced developments of industrialization and urbanization in the society lead to the decrease of birth rate. On the other hand, death rate stops dropping down to a certain degree; thus, the increase in population slows down. 4. As the civilization of the society continues, birth rate keeps decreasing and to a certain degree, turns into floating. Furthermore, though death rate stays stable, the growing numbers on elder people results in aging society. Total population starts to decline instead of continuing increasing.

     In the century, the changes in birth rate death rate of the R.O.C. also experienced the four phases; nevertheless, the R.O.C’s evolution of population is much faster than that of western developed countries. For instance, it takes European countries two hundred years to evolve from the phase of high birth rate and high death rate to the phase of low birth rate and low death rate, while it only takes Taiwan sixty years to finish the transition. More surprisingly, Taiwan’s birth rate continues to drop down, and enters to the stage of “lowest-low birth rate,” which is lower than the birth rate of western countries. In addition, the prolongation of life expectancy leads to rapid population aging. In 1994, the proportion of elder population in Taiwan was 7%, which fits WHO’s definition of aging society, and it is expected that to 2019, the proportion of elder population will reach 15% in Taiwan, which fits WHO’s definition of super aged society.

     Why does the population of the R.O.C. change so rapidly in the hundred years? What kinds of economic and social systems cause the rapid change? Otherwise, what kinds of policies lead to it? How do the fast changes in birth rate and death rate influence the society’s age and gender composition, and even the economic and social condition of the R.O.C? To discuss these questions, the following divides the transition of birth rate and death rate into three phases, including 1. Pre-war stable population development phase 2. Rapid population transition phase 3. Rapid population aging phase.