Why has Volgograd become a target?

On Monday, in Volgograd, a passenger bus exploded. As a result, according to the latest news, six people were killed and dozens were injured. What were the aims pursued by the terrorists? How to resist such moves? How to ensure the safety of citizens and the state?

A member of the Commission on Security of the Moscow City Duma, Sergey Goncharov, spoke about what might be behind what happened.