Even I have lived in the United States for almost five years, it was my first time to visit Washington DC, formally Washington District of Columbia. The city is known as capital city of the United States. The city does not own state, it is just an area so it does not have many populations. For major cities on recent days, it is pretty unique that it does not have a lot of population, although it has government of the United States which has tremendous effects internationally and also it is known as important financial center. The city also has a lot of museums and memorial statues.
Compare to the capital city of Japan, Tokyo. It was completely different. As I mentioned above ,Washington DC has a lot of historical places to visit and less population. However, in Tokyo, it is one the most urbanized city in the world. Even Japan has independent history and culture, Tokyo does not have many historical things. Unlike Washington DC, Tokyo is the highest population and population density in Japan.
In my opinion ,the capital city does not necessary to be the most urbanized or highest population in the country. In order to represent the country internationally, they need culture and history. Washington DC is the perfect city as capital city of the United States. The city is full of American culture and history and less population density, the city seems more cleaner than most of the cities in the United States. On the other hand in Tokyo, there are some historical places but not many as Washington DC, most of the places destroyed to be urbanized or developed. Tokyo has many crowds that the most of the foreigners would surprise, and those population density shows the city less cleaner and mess. With having Olympics in 2020 in Tokyo, they should be cultural and historical city instead of being urbanized more.