homogeneous = made up of the same types heterogeneous = made up of different types

Homogeneity isn't about race. It's not about the colour of your skin or the shape of your face, but about how you feel in relation to others in your society. In Japan there is a strong sense of cultural identity, and there as not so much diversity of opinion, belief, and behaviour as there is in other nations.

Both Rick and Su.Ki are correct in their answers. To apply the meanings of the words in your context, Japan has a very small ethnic mix, there are some Ainu on your northern island and a few European and other Asian communities. Here is what https://www.cia.gov/library/publications/the-world-factbook/geos/ja.html says about Japan. Shintoism 83.9%, Buddhism 71.4%, Christianity 2%, other 7.8% So you could say that was homogeneous, you basically have a shared religion as those classes must overlap. Compare that with my country Australia - Protestant 28.8% (Anglican 17.1%, Uniting Church 5.0%, Presbyterian and Reformed 2.8%, Baptist, 1.6%, Lutheran 1.2%, Pentecostal 1.1%), Catholic 25.3%, Eastern Orthodox 2.6%, other Christian 4.5%, Buddhist 2.5%, Muslim 2.2%, Hindu 1.3%, other 8.5%, unspecified 2.2%, none 22.3% And that 25.3% of Catholic people are probably from Ireland and Southern Europe not England. So it is quite a different cultural and genetic mix. You could describe that as heterogeneous. In my example, it is heterogeneous in religion.