Well, I sort of agree with you, SLX and YGIFS.
As I, and many sociol anthropology and current days sociologists see it, it's sort of a combination of all of the above. In a off shoot but related topic, serial killer numbers shot up in the US after the completion of the interstate highway system. We're people serial killing before, most certainly. Was it JUST the interstate, nope, news coverage and cross jurisdictional engagement also occurred at the same time as an ability for serial killers to be far more mobile and heavier traffic cross state. All if that made it easier to "hide" or commit acts further from home.
So, were language and racial variations a reason for early man's "war" or violence on others tribes. Absolutely. I want to be careful here as I don't recollect the specifics, but iirc our "pre-current day human ancestors" might have proactively worked to irradicate earlier "verision" of humanity. I actually recall hearing a hypothesis that that might be where a part of "trolls" and other similar creatures originated from in our lore. (Don't hold me too accountable on the specifics, it's Sunday am and I'm on my 1st cup of coffee).
Now, given that, or move past agricultural during the industrial revolution, bigger cities in which racial divides/violence were FAR more prevalent, a bigger new cycle, the larger economical reach and ultimately a global economy... the increased violence makes sense in a very ironic way. When you couple all the factors the 3 of you mentioned and cross it with an ever growing large corporate oligarchy globally AND a news feed that is heavily incentived to report "scary" things of all sorts for clicks/viewers etc... well.
How do you controll a population as the power structure? How do you do it globally?
Use the old tried and true, race, religion and other factors to distract from the real money factors underlying it. Make the plebes fight one another over whatever to keep them from looking up the chain at the real cause. At the same time use these fears to make them focus on one another to try and reduce one anothers freedoms for your own oligarchy aims. Easier to control.
A Renaissance Florentine Republic dude wrote about it long ago.
If I sound like a conspiracy theorist... well, I guess I am. However, most here and elsewhere largely agree the silent majority in the US is the one never heard over the squeaky wheels of the extremes on either side.
... that's part is NOT a conspiracy I came up with on my own.