(Credit to RealLifeLore whose video I watched and summarised)

For over 100 years japan has been one of the most powerful civilizations in the world. Its impact on culture has been absolutely astonishing. But its geography is terrible and this is why.

For ever, Japanese civilization has been built around the Tokyo plain, a huge empty field that is one of the only habitable and farmable regions in Japan. Nearly 85% percent of Japan is a huge mountain range that is either extremely expensive to habitat or absolutely impossible for humans to live in. This is Japans largest geographical problem, but they have a solution.

Since WW2, the Japanese government have been raising the general standard of living for the whole population, resulting in a lower birth rate and less population growth. This means that they will have enough time to terraform the mountains.

So in conclusion, Japan will probably be okay.