"Buku ini menggambarkan tentang pemerintahan Jepang di abad lalu."

Translation: This book describes the Japanese government in the last century.

[glhaynes90]

What is the difference between pemerintah and pemerintahan in this context?

[joeldipops]

https://kbbi.web.id/perintah

I'm not going to try to translate any of those huge blocks of text but the important distinction seems to be

pemerintah: sistem ... mengatur kehidupan sosial, ekonomi, dan politik suatu negara atau bagian-bagiannya;

System of organising society, economics and politics of a country or part of a country.

pemerintahan: proses, cara, perbuatan memerintah
The process, method or action of governing.

So I guess the second could be translated as "Governance" rather than "Government"