A good book for the history of it is The Gun (https://www.amazon.com/Gun-C-J-Chivers/dp/0743271734). Its essential point is that weapons of war are usually very durable goods, and outlive the geopolitical purposes for which they are produced and originally distributed. Kalashnikov-family rifles happen to have arrived in particularly unstable places.
EDIT: Weapons built by local forces tend to be more... idiosyncratic. Though compatibility with AK ammunition is a desirable feature. https://atwar.blogs.nytimes.com/2012/08/08/taliban-gun-locke...
Also, another example of this durability is the Humvees that have ended up in Syrian government hands after going through three different owners - US, Iraq, ISIS, Syria.
The Kalashnikov had been designed in 1947, (hence, AK-47), but it took more than a decade before a bug-free version (the AKM) was considered reliable enough to make standard-issue. (When this article refers to "AK-47s", most of the actual weapons involved were actually AKMs.)
The US, by contrast, had spent the decades since WWII resisting the assault rifle concept, so that when Vietnam rolled around their fantastically rich and well-funded military found its infantry outgunned by peasant militias wielding second-hand Soviet rifles. So the rifle went from initial acceptance, including these kinds of stupid last-minute design changes that are common in any project, to large-scale combat deployment within a year; normally, there would have been years of incremental usage to catch these bugs, but the rifle was so desperately needed that it was rushed to the front.
A book I've recommended in another thread, which gives a great introduction to the history and impact of the Kalashnikov in particular and assault rifles in general, is C.J. Chivers's "The Gun" (https://www.amazon.com/Gun-C-J-Chivers/dp/0743271734), or this shorter-form article he wrote in response to recent msas shootings (https://www.nytimes.com/interactive/2016/world/ak-47-mass-sh...)
I read it not so much as a historical text but as a story about dramatic shifts in power attributed to technological advancement and strategy.