Here's an interesting examination of language by Will H. Moore:

I was interested in tracking several words that the research and reading I have done during my career has led me to note that government officials use to describe “dissidents.” So I plugged the words “bandits,” “communists,” “guerrillas,” “insurgents,” “rebels,” and “terrorists” into Chronicle and produced the graph below.

Here's his takeaway:

We see that the US Civil War produced an enormous use of the word “rebels,” and though the count today is a much smaller percentage of the total number of words published in the Times, ... we see that “rebels” grew dramatically in prominence in 2011. “Communists” first appears around 1918, and then explodes after 1945. The impact of 9/11 upon the word “terrorists” is equally prominent.