The answer is - the monsoon climate regions of Asia.
The most crowded living conditions in Asia are in the monsoon climate regions of the continent. From southern Pakistan, through the eastern part of India, Bangladesh, and eastern part of China, we have the most heavily populated places in Asia, where we have populations in a total of more than 2 billion people. This is because in this part the climate is most suitable for the people, usually, they are places close to the sea, there's abundance of big rivers, and this places historically for thousands of years have a tradition of being very heavily populated.