Each of these graphs plots over time the fraction that one word constitutes of all words in books mined from the Google Books project.
Westward expansion of the U.S.
One invested in railroads, the other, canals.
New religions of the last 200 years.
Note how people didn't start capitalizing "black" until the mid '60s, even though it had been used as a descriptor as often as "colored" for a long time. Note the different curves for "negress" and "Negress." Capital "Negress" rose in usage alongside "Negro woman" and was nearly as common in the '40s, but half as common in the '70s. Lowercase "negress" was mostly replaced by capitalized versions, which were then replaced as well.
Industrialization of food.
Pawpaws were more popular than blueberries, and gooseberries were more popular than raspberries!
Notice how HIV lags AIDS, and condom is correlated more with HIV than with AIDS.
Israel and Palestine as a people and as a place
The names of Muslims
It's 2:00 AM, and there's still worlds to explore just off the top of my head. This is a treasure trove. Google Books Team, this is an amazing accomplishment. I used to envision that this is how history would be done in 50 years when the digital age has ensured that anything that someone cares enough about to transfer is preserved. Now we're getting to do that sort of history, today.