You could invest $1000 right now and it might do 8% again in the next 100 years.
Looking back though, there are a few interesting things to consider
-There were no index funds in 1916. The only choices were individual stocks, which can be quite risky. Here are some stocks from the DOW in 1916, although most didn't fail catastrophically. AT&T in particular is really healthy today.
American Beet Sugar, American Can, American Locomotive, AT&T, Baldwin Locomotive, Goodrich, Republic Iron, Studebaker, Texas Company, Utah Copper, Western Union, Westinghouse Electric
-There were plenty of reasons to be afraid from the beginning. The market was actually closed right after WWI started. From the beginning of 1916 to the end of 1920 the market had dropped 50%. Then afterwards there was the Great Depression, World War 2, and the Cold War. Certainly a lot to worry about!
-Purchasing stocks was more difficult. I'm not sure how it worked exactly but I think you had to go in person to a brokerage with cash.