Writings have always reflected the spirit of the times in the history of mankind. People write down what they care about at the moment. And it is obvious, that there are trends in the literature. Trends of certain topics that get interesting suddenly. Google has published a tool called Ngram some time ago. With this tool it is possible to search all (or almost all) books indexed by Google by keywords.
Unsurprisingly, world events have always influenced literature. For example, the mention of the country “Saudi Arabia” in books suddenly increased beginning at the year 1985. This is certainly caused by the 1. Gulf War, which began in 1980 , as well as to the oil crisis , in which Saudi Arabia was involved.
Interesting to see is also the boom and the fall of the term “artificial intelligence” . While this term was used in the mid- 80s quite often, the usage rapidely decreased in the mid-90s. A relatively new trend is Facebook, here the citation have increases in the past few years.