Travel warnings, alerts, and emergencies: How the U.S. decides it’s too dangerous to go

In 2012 the U.S. State Department warned travelers about the dangers of visiting 33 countries, spanning from Algeria to Yemen. Some warnings simply suggest exercising caution while others are “no go” warnings, baldly stating that you shouldn’t visit.

... Most information comes from field officers, and their reports are combined with intelligence filtered from various governmental agencies by the State Department's Bureau of Diplomatic Security. The Citizen Services team coordinates the overall process, and O'Brien has to sign off on every travel warning before it's publicized.

"But alerts and warnings are not usually a Washington, D.C.-top-down-sort-of-thing," he adds. "The genesis usually comes instead from embassies and consulates overseas, who have contacts in law enforcement, government and media on the ground."