“The only gun shop in all of Mexico is behind a fortress-like wall on a heavily guarded military base. To enter the Directorate of Arms and Munitions Sales, customers must undergo months of background checks — six documents are required — and then be frisked by uniformed soldiers.” If there’s only one gun store in Mexico, then why is gun violence soaring? Here’s a hint: “On this issue, like so many aspects of life in Mexico, the influence of its powerful neighbor to the north is keenly felt.”