I am not sure when the designated hitter rule started to become a force for modernizing North American society.
I have read actual English-language articles on this topic in which the notion of spreading the DH to the National League is mentioned as a mechanism that would modernize baseball.
I don't think it's quite that clear-cut. It's not like an invention that changed the quality of life in the way that the advent of the twist-off cap made life easier for beer vendors at the ballpark.
Granted, the DH is newer than the game itself. The DH rule is just 43 years old, whereas there are records of the ancient Egyptians playing a game with a ball and a stick thousands of years ago. And that game with a ball and a stick was not golf.
The short history of the origins of the DH is this: More than four decades ago, American League owners thought that there wasn't enough offense in the game, so they came up with having a (designated) hitter replace the pitcher. One more hitter in the lineup, one less likely out; therefore more runs.
The NL owners thought this was a cheap gimmick, beneath the dignity of the grand old game, and they did not go along with the DH.
Time has softened the stance of some NL officials. In the past, they thought the DH was heresy. They now think that the DH is merely unnecessary.

There was a brief DH boom last week, when Commissioner Rob Manfred discussed the pros and cons of the NL adopting the DH. This was seen in some quarters as a signal that the DH was on its way to all 30 clubs.
In an interview this week with Jerry Crasnick of ESPN.com, Manfred clarified the situation.
"The most likely result on the designated hitter for the foreseeable future is the status quo," the Commissioner said. "I think the vast majority of clubs in the National League want to stay where they are."
And so, at least temporarily, western civilization has once again been saved.
Just kidding; at least a little. There is no moral high ground available in this sort of discussion. The difference between the DH and the non-DH game is more subtle than that. The NL game preserves the multilayered decision making that can go into merely making a pitching change. The AL game kicked that thought-provoking, intriguing stuff to the curb 43 years ago and never looked back.
The idea that the game could not persist while playing under two sets of rules used to have some adherents. But now, with the game at record-setting levels of popularity when measured by attendance, local TV ratings and, frankly, revenue, it looks like baseball has not notably suffered for playing under two different sets of basic personnel groupings.
There is a distinct difference between the games played by the AL and the NL. But this is not the stuff of a great ideological divide.
The DH has given us stars that otherwise would not have shone quite as brightly. David Ortiz of the Red Sox comes first to mind in the contemporary game. As a first baseman alone, he wouldn't be headed on his present course toward the Hall of Fame.
One anti-DH argument -- that it rewards people who are one-way players -- used to have some currency. But anti-DH types are no longer as vehement about it. Pitchers are also routinely rewarded for being one-way players, although they are asked to pick up a bat and perform the other half of the job.
But don't tell me that the DH is inherently progressive. In total, the DH argument represents an aesthetic judgment about whether a layer of managerial decision-making is worth the price of sacrificing offense by allowing the pitchers to attempt to hit. The one league said no and changed. The other league said yes and stayed the same.
Baseball has survived this disagreement so far. In the interests of tolerance and harmony, let the AL keep the DH, as long as the NL isn't forced to sacrifice the subtle beauty of a game with no designated hitter.