Q. Our organization just had a raging dispute about the use of the term “the 1910s.” This term is actually going to be used in a photo caption in a book. I’m astounded! What do you think of this?

A. I think it’s the way CMOS styles it in paragraph 9.33 (“Decades”):

To refer to the second decade (i.e., without writing “second decade”), prefer numerals (e.g., 1910s); the expression “the teens” should be avoided, at least in formal contexts.