Thankfully there were two crime waves during the 20th C, so we can tell whether it really was related to rising violence levels or was just a spurious correlation from the past couple decades. If I'm right, there should've been a lot of candy innovation from 1900 to 1933, and particularly during the second half of that period (just as the later '70s through early '90s were more creative than the '60s and early '70s). The further into falling-crime times of 1934 through 1958, the lower the innovation should drop. Later I'll look at the 1960 and after period.
There may be some more systematic, quantitative way to show that the hunch is right, but for now I'll just go through the major candy brands introductions by year. I'm leaving out pre-1900 brands since we don't have homicide rate data to put them in rising or falling-crime times. What's "major" is just my call for now; one rule of thumb is to exclude candy that you would only buy on special occasions, like at the movies. I'm focusing less on gum and pure sugar candies, more on main category of products with chocolate, nuts, etc.
Here's a chart showing the introductions in 5-year chunks, the first and second half of a decade, with the mid-year across the bottom:
|Dum Dum Pops|
|Milky Way||Heath bar|
|Butterfinger||Reese's PB Cups|
|Charleston Chew||Dubble Bubble||PayDay||Nestle Crunch|
|Baby Ruth||Raisinets||3 Musketeers||5th Avenue|
|Mounds||Milk Duds||Tootsie Pops||Sugar Babies||Whoppers|
|Oh Henry!||Sugar Daddy||Zagnut||Kit Kat||M&M's||Almond Joy|
|Clark bar||Turtles||Mr. Goodbar||Snickers||Life Savers||Pep. Pattie||Bazooka||Peanut M&M's|
The first Hershey bars were introduced before 1900, so that's why they're not shown. Sure enough, though, there isn't too much going on until the later half of the rising-crime period. The peak is clearly the Roaring Twenties, not only by number of brands released but also weighting them by how influential they would become in American candy culture. Even the early '30s did well, if for no other reason than that Snickers has been the dominant candy bar in America and many other countries.
Already by the later '30s, there's a noticeable drop-off. The Nestle Crunch and Kit Kat bars came out then, but they still aren't as popular as Snickers and 3 Musketeers, from the earlier '30s. The '40s were even less inventive except for M&M's, and maybe Whoppers. Even less creative were the '50s, saved only by an extension of an existing brand, Peanut M&M's. The later '50s saw the Pez dispensers with the famous heads on them, although the candy and basic dispenser were invented long before, so I left that off the chart.
So far the idea checks out -- creativity tracks the trend in the crime rate for another domain, where we might not have even expected it, and however silly the example may seem. Next time I'll look at 1960 through today.