When you look at the Law of Kamma, there is this aspect of considering that if somebody has harmed someone today then in the future they are supposed to experience some harm themselves. That means another person has to harm them. And then that person who harms them, has to be harmed by someone else. So if you look at it in this way, there is this seemingly endless cycle of cruelty, of people getting harmed.
Now - as to whether it ends or whether it does not end - I can't say. One way to look at the possibility that it will end is to say, "Okay, if somebody beats me up and breaks my legs, that could mean that they will get beaten up and they will have their legs broken as well in some future time. But - wait a minute! Can they get beaten up in a way that is not done by a human? Can they possibly be walking along and a mountain avalanche starts and beats them up in the same way that they hit me and broke my legs?
So maybe there will be an ending to the cycle one day. That people could suffer the results of their bad Kamma and yet in a way that is not directly from another person, so that another person does not make more cruelty. You have to let your imagination go on that one, it seems to be quite possible.
But whether it's ending or whether it's not ending, the fact is that we look back at ourselves. Can we end the cruelty that we make? Can we stop being cruel, can we stop being angry? Can we stop doing things that harm other people? That's the practice. Whether the world changes or not - that's beyond us. The Buddha never said it would or wouldn't. So come back to your own practice and then you won't get so caught up with doubts about whether the world is going to end, or cruelty ends and so on.
The question itself is actually more Dukkha - getting caught up in it. This is more of the Dukkha. So we let go of that and simply say, "I don't know. And I can live with it. I don't know". But what you do know is whether you are Compassionate today, whether you are angry today and so on. Those are things you can work on.