This kind of violence hasn’t been common in other parts of the world for centuries. It’s also a phenomenon that is distinct to states in South East Asia - and, in fact, to the Buddhist states in South East Asia ( it was not practiced in what is now Malaysia in Indonesia - which are now Muslim and before that practiced a religion that mostly resembles Hinduism).
Just living in any of these countries, one will see the constant effort of people, even hustling, to get ahead in life, far from any fatalistic conceptions one might have about their life.
I can, in fact, think of other examples of worse brutality, even in the last few centuries, for instance the American slave system and treatment of labourers in Congo. Not quite the same extent, but still terrible, the British had an indentured labour system transporting Indians whose local lands were devastated by colonial rule. I wouldnt casually attribute these to religion of the westerners.
Lets look at some of your points
> 'not despite Buddhism but because of it.'
This is your main thesis and to support this you say -
> At least these two make a point of encouraging charity and kindness towards others.
Directly, (not subtly), implying that Buddhism does not do this.
A basic search would give you something like the basic virtues of Buddhist teachings - https://en.wikipedia.org/wiki/Brahmavihara and how these virtues are popularized via stories where the protagonist gives up lives to save tiger cubs or say, the story of Angulimala.
Note that there is no condemnation of non-believers to eternal hell - a belief which has caused tremendous violence and looks at lot of cultures as essentially devil's work- a belief is still not repudiated today (it cant as it is a core doctrine).
Also, modern industrialized societies are still having a hard time accepting an elementary insight that animals can suffer intensely and creating montrosities where this is noted quite early in Buddhist and similar traditions.
> misfortunes such as being born poor (or worse) are seen as being justified somehow
Another point you bring up is karma and the word you use is 'justified'. When a thief or a killer attacks and causes suffering to a Buddhist, they might take it as the result of past bad karma, but that doesnt make the action 'justified'. Indeed, that action itself generates bad karma. A ruler inflicting suffering on people also gets bad karma.
The notion that people are fatalistic about misfortune is false can be seen at multiple levels -
Firstly, at the whole point of the tradition itself is to overcome karma, secondly, popular cultures are filled with practices aimed at changing karma.
At the political level, try reading James Scott on how peasants resisted states which became tyrannical https://www.amazon.com/Art-Not-Being-Governed-Anarchist/dp/0...
A more subtle but important point is that 'justification' is bringing in a different framework - the notion of normative ethics which is inherited from Christianity - whereas the concept of karma is seen more like a natural property like a bodily sickness.