Specifically, SWAT teams didn’t exist until the 1960s. I’d wager their escalated use against civilians in their homes likely coincided with the War on Drugs in the 1980s.
https://www.policemag.com/weapons/article/15348048/how-the-n...
Of course, there must have been many other causes. It wasn’t the first time in US history that police were outgunned.