The Google Centuryshare Calculator [ http://blog.outer-court.com/centuryshare/ ] stores the Google page-count for all years of the 20th Century (from 1900-2015). Submitting a query, like "Beatles", or "Cold War", it will then query Google (via the Google Web API) for the number of pages for a year plus the keyword. Finally, the percentage of those pages, compared to those each year without keyword, is shown in a diagram.
For example, the peak for "Chernobyl" is clearly 1986, while other keyphrases -- like "Rolling Stones" -- show more of a soft wave form.
Note that you need the Google Web API key to use the tool (it will need 20 Google queries per calculation).