3reasons why japan is so densely populated?

Japan is densely populated because it is an island nation which means that there is not a lot of territory for the Japanese to spread out and inhabit. In addition Japan has a large population for the small territory that exists. A final reason is that much of life in Japan is centered around urban zones, which means that most of the population lives in these urban environments which are very dense. 

Ihave no idea what the answer is