The correct answer to this open question is the following.
The correct answer is because of manufacturing and urbanization.
Cities were formed in East Asia because of manufacturing and urbanization. This means that after many years of farming and rural life, people in East Asia wanted better life opportunities and industries offered them this chance. So people started to leave the rural areas and immigrate to the places where industries and manufacturing were located. This way, more and more people started to work in these areas that grew hand in hand with the industry in the services were needed or this number of people such as markets, stores, housing, and schools.
East Asian countries such as China, Korea, and Japan evolutionary under this environment and under the influence of European countries that arrived at their territories.