France is massing some 70,000 police officers ahead of a possible new wave of unrest, with armored vehicles and water cannons lined up in support. The scale of the deployment suggests the authorities expect confrontation on the streets rather than calm marches. On social networks, sympathizers of radical left movements have been openly encouraging acts of violence and looting. Those online appeals are being watched closely by security planners in Paris. The country has been through several rounds of serious rioting before, which shapes how police stage their resources for days like these. Neither an exact date nor the event that might set off the trouble was named in the available details.