Here is a Spanish Google Ngram for law, politics, religion,economy, and the press.
These kinds of graphs don’t necessarily show what was most important to most people, but do they show what writers and readers of books were interested in, or where the main disputed questions lay.
For the Spanish terms, the first thing of interest is the steep decline for terms associated with law (the blue line) and the steep incline for terms associated with politics (the orange line). The two lines diverge sharply in about 1934, and politics peaks in about 1990. I haven’t seen anything similar in other languages. The other lines are unremarkable. As for possible reasons, the first thing that comes to mind is the Spanish Civil War (1936-39). Then there were political revolutions and coups in Latin America, including the Reagan-era support for counter-revolutions. I have no explanation for the decline of interest in law.
In English, politics (orange line) begins a steady rise in about 1927, but law (blue line) remains stable, unlike the Spanish graph. Religion (green line) declines badly, of course. This doesn’t necessarily mean people had lost interest in religion. It might be more that there aren’t as many unresolved questions or controversies anymore, at least as compared to around 1830, when interest in books dealing with religion was very high. This was the time of the Second Great Awakening.
What explains the rising interest in politics in English-language books starting in about 1927? The capitalist/fascist/socialist tensions no doubt relate to this.
One reader pointed out that
the massive rise in the occurrence of “política” might be that this word also stands for “policy” in non-political contexts. A hospital might therefore have a “política de zona libre de humo”, a business might have a “política de seguridad laboral”, and so on.
So I did another search using politico + gobierno, along with ley + legal. This is the result:
Thank you to Jochen Kleinschmidt for this Facebook comment:
This is interesting. The “takeoff” of politics now seems to coincide with the military coup in Brazil in 1964, reaching a peak with the gradual replacement of military regimes in the mid-1980s. In other words, with the new search criteria, actual structural changes in the political system might become visible.