TheBrilliantMistake
^There is more violent crime per capita in the US than the UK - considerably more.
However, each country's method of logging and categorising such crimes can differ, so it's not always a perfect match / like for like.^
Actually, I would have thought it was relatively easy to compare as, firstly, we are comparing violent crime, definitions of which are similar everywhere, particularly so when comparing between two common-law jurisdictions. I expect there is a comparison somewhere. Do you have one? If you don't, don't make the claim.
As for South Africa, gun ownership and crime is so poorly recorded that their statistics can't be relied on. The police routinely don't investigate crimes because they are under-resourced, disorganised and bribable. For historical reasons, there is a culture of suspicion of the government, and therefore gun control is routinely circumvented. And finally, there is corruption in the government too, so a 21% drop in (what exactly?) could simply be the government instructing their statisticians to release a good news story.