Apartheid in South Africa was ended because nations chose individually to apply sanctions to oppose the inhuman conditions in the country. You don’t need world police to enforce international law, it has meaning and substance through countries choosing to stand up for decency.
Without international law, and rubbishing standards of decency as meaningless without a global world police, leads down a very dark path. The horrors of the mid 20th century, like the holocaust and atrocities committed by Japan, among many other examples, happened under a might makes right mentality. Many international laws about crimes against humanity were a response to this to prevent it being repeated, because it is utterly horrific
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