PARIS—Every Friday, Johanna Bettach, a pregnant mother of two, stocks up on weekend supplies at the Hyper Cacher supermarket. Last week, just before she was getting ready to shop, an Islamist militant gunned down four Jewish customers at the kosher store and took many others hostage.

The Hyper Cacher attack, one of the deadliest against France’s Jewish community since World War II, spurred outrage across the country. It was by no means isolated, coming against a backdrop of acts of violence and intimidation.

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