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 9.35 (on decades):
As for the second decade, “the teens” may be used in casual prose, but in formal contexts either “the second decade” or numerals (e.g., “2010s”) should be preferred.