explain which theme, region, and period a historian would focus on to learn about parisian music 100 years ago

The theme would be French culture, and more specifically, Parisian culture from 100 years ago. In culture, the historian would include not only music, but also paiting, theater, cinema, and so on.

The region would obviously be Paris, but also other regions of France, and even other countries, where Parisian music from the time might have had an influence.

And the period would be the first two or three decades of the XX century, which is the period that led to the development of Parisian music from 100 years ago.