Mental illness? “Right-wing extremism”? Maybe. There is also one other possibility: the Islamic State issued this call in September 2014:
So O muwahhid, do not let this battle pass you by wherever you may be. You must strike the soldiers, patrons, and troops of the tawaghit. Strike their police, security, and intelligence members, as well as their treacherous agents. Destroy their beds. Embitter their lives for them and busy them with themselves. If you can kill a disbelieving American or European — especially the spiteful and filthy French — or an Australian, or a Canadian, or any other disbeliever from the disbelievers waging war, including the citizens of the countries that entered into a coalition against the Islamic State, then rely upon Allah, and kill him in any manner or way however it may be….If you are not able to find an IED or a bullet, then single out the disbelieving American, Frenchman, or any of their allies. Smash his head with a rock, or slaughter him with a knife, or run him over with your car, or throw him down from a high place, or choke him, or poison him….
“Eight stabbed in Russian city, police shoot man dead,” Reuters, August 19, 2017:
MOSCOW – Eight people were injured in a knife attack in the Siberian city of Surgut, Russian media agencies reported, citing the spokesman for the local office of the Russian law enforcement committee.
“A man was running along the main streets stabbing people,” TASS reported….