What does Buddhism say we should do about injustice/cruelty?

I've been trying to work on my biggest hindrance on the Buddhist path, which is anger. Meditation has helped me a lot when it comes to anger over small things that aren't worth being bothered by (people being rude, not getting what I want, getting what I don't want, etc.) I agree that you should treat people with kindness and respect, but also understand that you're not entitled to always get the treatment you want.

However, I find myself getting angry over bigger and more significant problems. Specifically, corruption in government and the suffering it causes to poor and innocent people. This happens in my country and all over the world. Evil people rise to power and they cause violence, injustice, homelessness, lack of food/medicine to the innocent; while the evil hoard all the money and resources that the poor actually need. This makes me so angry and think thoughts that aren't very Buddhist. Such as, "I know Buddhists should be non-violent, but I think some people in power deserve violence done to them. It'd only be their bad karma finally catching up with them, especially if they've lived a life of oppressing people."

I know this there must be a wiser perspective than this, which is why I'm making this post. What does Buddha say we should do about evil rulers? What would Buddha say about one's desire for them to be punished or for them to get the suffering they deserve?

I know Buddhists have been oppressed throughout history in countries like Vietnam, Cambodia, and Tibet. I've heard stories about monks being kept prisoner, starved, tortured, and still being totally at peace and undisturbed within themselves. This seems impossible to regular people like me. What wisdom do they understand that most don't?