US basically has a firearms license but by exclusion. Anyone with felonies or DV violations can't have guns, neither can illegal immigrants, neither can drug users . There are probably fewer Americans that can legally buy ammo and guns than Canadians by %.

If you use the ATFs guidelines on what is considered a prohibited person, it likely applies to about half of all US adults that are prohibited from buying ammunition. This when you consider ~30+% of US has used cannabis/fentanyl/etc or misused a prescription drug in the past year, the insane number of people we've made felons, the fact that restraining orders are now practically part and parcel of divorce negotiations as leverage (permanent restraining order bars you from owning guns), and then the fact that DV convictions are incredibly common in USA (police automatically arrest someone if they show up on a domestic complaint), then add the illegal immigrant population on top of that.