Based on what metric are you making that claim? Canada, for example, certainly still has an issue with firearm related crimes [source]. It is also quite arguable that firearms laws even have an effect on reducing crime in general [source] (I will concede that this source, the fraser institute, isn't the most reliable, but their data does show some interesting things that cannot be ignored). Furthermore, it has been reported that the majority of handgun related crime, in Canada, is done with handguns that were illegally owned -- they were smuggled in from the USA.
One could point to some trends of firearms rates decreasing and attributing them to firearms bans, but the devil is often in the details. For example, this study by Rand stated that firearms related crimes in Australia were already on a downward trend piror to the 1996 buyback, and similar dips in violent crime can be seen many other western countries that didn't adopt such strict gun-control measures -- violent crime, in general, appears that it has been on a downward trend for quite some time.